Is there a closed form for the sum of the cubes of the binomial coefficients?
We know that
$$
sum_{k=0}^n binom{n}{k} = 2^n;; text{ and };;
sum_{k=0}^n binom{n}{k}^2 = binom{2n}{n}
$$
hold for all $nin mathbb{N}_0$.
Now I tried to find a similar expression for
$$
sum_{k=0}^n binom{n}{k}^3
$$
but didn't get anywhere at all. What I found were only asymptotic estimates (see Sum of cubes of binomial coefficients or Asymptotics of $sum_{k=0}^{n} {binom n k}^a$).
Now is there a closed form for this sum or, what would be even better, for $sum_{k=0}^n binom{n}{k}^alpha$ with any $alpha in mathbb{N}_0$?
combinatorics binomial-coefficients closed-form
add a comment |
We know that
$$
sum_{k=0}^n binom{n}{k} = 2^n;; text{ and };;
sum_{k=0}^n binom{n}{k}^2 = binom{2n}{n}
$$
hold for all $nin mathbb{N}_0$.
Now I tried to find a similar expression for
$$
sum_{k=0}^n binom{n}{k}^3
$$
but didn't get anywhere at all. What I found were only asymptotic estimates (see Sum of cubes of binomial coefficients or Asymptotics of $sum_{k=0}^{n} {binom n k}^a$).
Now is there a closed form for this sum or, what would be even better, for $sum_{k=0}^n binom{n}{k}^alpha$ with any $alpha in mathbb{N}_0$?
combinatorics binomial-coefficients closed-form
2
Its been proven no closed formula can exist
– Jorge Fernández
Nov 28 at 18:05
1
on a positive note, if you add $(-1)^k$ to you sum of cubes, there is closed formula called Dixon's theorem: mathworld.wolfram.com/DixonsTheorem.html
– Abdelmalek Abdesselam
Nov 28 at 18:32
add a comment |
We know that
$$
sum_{k=0}^n binom{n}{k} = 2^n;; text{ and };;
sum_{k=0}^n binom{n}{k}^2 = binom{2n}{n}
$$
hold for all $nin mathbb{N}_0$.
Now I tried to find a similar expression for
$$
sum_{k=0}^n binom{n}{k}^3
$$
but didn't get anywhere at all. What I found were only asymptotic estimates (see Sum of cubes of binomial coefficients or Asymptotics of $sum_{k=0}^{n} {binom n k}^a$).
Now is there a closed form for this sum or, what would be even better, for $sum_{k=0}^n binom{n}{k}^alpha$ with any $alpha in mathbb{N}_0$?
combinatorics binomial-coefficients closed-form
We know that
$$
sum_{k=0}^n binom{n}{k} = 2^n;; text{ and };;
sum_{k=0}^n binom{n}{k}^2 = binom{2n}{n}
$$
hold for all $nin mathbb{N}_0$.
Now I tried to find a similar expression for
$$
sum_{k=0}^n binom{n}{k}^3
$$
but didn't get anywhere at all. What I found were only asymptotic estimates (see Sum of cubes of binomial coefficients or Asymptotics of $sum_{k=0}^{n} {binom n k}^a$).
Now is there a closed form for this sum or, what would be even better, for $sum_{k=0}^n binom{n}{k}^alpha$ with any $alpha in mathbb{N}_0$?
combinatorics binomial-coefficients closed-form
combinatorics binomial-coefficients closed-form
edited Nov 28 at 17:58
amWhy
191k28224439
191k28224439
asked Nov 28 at 17:56
bruderjakob17
1487
1487
2
Its been proven no closed formula can exist
– Jorge Fernández
Nov 28 at 18:05
1
on a positive note, if you add $(-1)^k$ to you sum of cubes, there is closed formula called Dixon's theorem: mathworld.wolfram.com/DixonsTheorem.html
– Abdelmalek Abdesselam
Nov 28 at 18:32
add a comment |
2
Its been proven no closed formula can exist
– Jorge Fernández
Nov 28 at 18:05
1
on a positive note, if you add $(-1)^k$ to you sum of cubes, there is closed formula called Dixon's theorem: mathworld.wolfram.com/DixonsTheorem.html
– Abdelmalek Abdesselam
Nov 28 at 18:32
2
2
Its been proven no closed formula can exist
– Jorge Fernández
Nov 28 at 18:05
Its been proven no closed formula can exist
– Jorge Fernández
Nov 28 at 18:05
1
1
on a positive note, if you add $(-1)^k$ to you sum of cubes, there is closed formula called Dixon's theorem: mathworld.wolfram.com/DixonsTheorem.html
– Abdelmalek Abdesselam
Nov 28 at 18:32
on a positive note, if you add $(-1)^k$ to you sum of cubes, there is closed formula called Dixon's theorem: mathworld.wolfram.com/DixonsTheorem.html
– Abdelmalek Abdesselam
Nov 28 at 18:32
add a comment |
2 Answers
2
active
oldest
votes
These numbers are called the Franel Numbers. It's proven in (Petkovšek, M., Wilf, H. and Zeilberger, D. (1996). A=B. Wellesley, MA: A K Peters. p. 160) that there is no closed form for these numbers, in terms of the sum of a fixed number of hypergeometric terms.
However, as @Robert_Israel points out, the expression could possibly be represented by different types of closed form.
2
... if "closed form" is defined as "the sum of a fixed number of hypergeometric terms". There could be other types of "closed form".
– Robert Israel
Nov 28 at 18:24
@Robert Was just thinking that. Thanks for the suggestion.
– Jam
Nov 28 at 18:26
add a comment |
The binomial coefficient for a given pair of $n geq k geq 0$ integers can be expressed in terms of a Pochhammer symbol as the following.
$$
binom n k = frac{(-1)^k(-n)_k} {k!}.
$$
The expression is valid even if $n$ is an arbitrary real number.
Here we note two things.
- The Pochhammer symbol $(-n)_k$ is zero, if $n geq 0$ and $k > -n$.
- The factorial $k!$ can be written as $(1)_k$.
Using these observations, we can express your sums in terms of a generalized hypergeometric function $_pF_q$ as the following. For the sum of the binomial coefficients, we have
$$
sum_{k=0}^n binom n k = sum_{k=0}^n frac{(-1)^k(-n)_k}{k!} = sum_{k=0}^infty (-n)_k{frac{(-1)^k}{k!}} = {_1F_0}left({{-n}atop{-}}middle|,-1right).
$$
For the sum the square of the binomial coefficients, we have
$$
sum_{k=0}^n {binom n k}^2 = sum_{k=0}^n left(frac{(-1)^k(-n)_k}{k!}right)^2 = sum_{k=0}^infty frac{left((-n)_kright)^2}{k!} cdot frac{1}{k!} = {_2F_1}left({{-n, -n}atop{1}}middle|,1right).
$$
And for the sum of the cube of the binomial coefficients $-$ also known as Franel numbers $-$, we have
$$
sum_{k=0}^n {binom n k}^3 = sum_{k=0}^n left(frac{(-1)^k(-n)_k}{k!}right)^3 = sum_{k=0}^infty frac{left((-n)_kright)^3}{(k!)^2} cdot frac{(-1)^k}{k!} = {_3F_2}left({{-n, -n, -n}atop{1, 1}}middle|,-1right).
$$
In general, for a positive integer $r$, we have the binomial sum
$$
begin{align*}
sum_{k=0}^n {binom n k}^r &= sum_{k=0}^n left(frac{(-1)^k(-n)_k}{k!}right)^r = sum_{k=0}^infty frac{left((-n)_kright)^r}{(k!)^{r-1}} cdot frac{(-1)^{rk}}{k!} \ &= {_rF_{r-1}}left({{-n, -n, dots, -n}atop{1, dots, 1}}middle|,(-1)^rright).
end{align*}
$$
add a comment |
Your Answer
StackExchange.ifUsing("editor", function () {
return StackExchange.using("mathjaxEditing", function () {
StackExchange.MarkdownEditor.creationCallbacks.add(function (editor, postfix) {
StackExchange.mathjaxEditing.prepareWmdForMathJax(editor, postfix, [["$", "$"], ["\\(","\\)"]]);
});
});
}, "mathjax-editing");
StackExchange.ready(function() {
var channelOptions = {
tags: "".split(" "),
id: "69"
};
initTagRenderer("".split(" "), "".split(" "), channelOptions);
StackExchange.using("externalEditor", function() {
// Have to fire editor after snippets, if snippets enabled
if (StackExchange.settings.snippets.snippetsEnabled) {
StackExchange.using("snippets", function() {
createEditor();
});
}
else {
createEditor();
}
});
function createEditor() {
StackExchange.prepareEditor({
heartbeatType: 'answer',
autoActivateHeartbeat: false,
convertImagesToLinks: true,
noModals: true,
showLowRepImageUploadWarning: true,
reputationToPostImages: 10,
bindNavPrevention: true,
postfix: "",
imageUploader: {
brandingHtml: "Powered by u003ca class="icon-imgur-white" href="https://imgur.com/"u003eu003c/au003e",
contentPolicyHtml: "User contributions licensed under u003ca href="https://creativecommons.org/licenses/by-sa/3.0/"u003ecc by-sa 3.0 with attribution requiredu003c/au003e u003ca href="https://stackoverflow.com/legal/content-policy"u003e(content policy)u003c/au003e",
allowUrls: true
},
noCode: true, onDemand: true,
discardSelector: ".discard-answer"
,immediatelyShowMarkdownHelp:true
});
}
});
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
StackExchange.ready(
function () {
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fmath.stackexchange.com%2fquestions%2f3017475%2fis-there-a-closed-form-for-the-sum-of-the-cubes-of-the-binomial-coefficients%23new-answer', 'question_page');
}
);
Post as a guest
Required, but never shown
2 Answers
2
active
oldest
votes
2 Answers
2
active
oldest
votes
active
oldest
votes
active
oldest
votes
These numbers are called the Franel Numbers. It's proven in (Petkovšek, M., Wilf, H. and Zeilberger, D. (1996). A=B. Wellesley, MA: A K Peters. p. 160) that there is no closed form for these numbers, in terms of the sum of a fixed number of hypergeometric terms.
However, as @Robert_Israel points out, the expression could possibly be represented by different types of closed form.
2
... if "closed form" is defined as "the sum of a fixed number of hypergeometric terms". There could be other types of "closed form".
– Robert Israel
Nov 28 at 18:24
@Robert Was just thinking that. Thanks for the suggestion.
– Jam
Nov 28 at 18:26
add a comment |
These numbers are called the Franel Numbers. It's proven in (Petkovšek, M., Wilf, H. and Zeilberger, D. (1996). A=B. Wellesley, MA: A K Peters. p. 160) that there is no closed form for these numbers, in terms of the sum of a fixed number of hypergeometric terms.
However, as @Robert_Israel points out, the expression could possibly be represented by different types of closed form.
2
... if "closed form" is defined as "the sum of a fixed number of hypergeometric terms". There could be other types of "closed form".
– Robert Israel
Nov 28 at 18:24
@Robert Was just thinking that. Thanks for the suggestion.
– Jam
Nov 28 at 18:26
add a comment |
These numbers are called the Franel Numbers. It's proven in (Petkovšek, M., Wilf, H. and Zeilberger, D. (1996). A=B. Wellesley, MA: A K Peters. p. 160) that there is no closed form for these numbers, in terms of the sum of a fixed number of hypergeometric terms.
However, as @Robert_Israel points out, the expression could possibly be represented by different types of closed form.
These numbers are called the Franel Numbers. It's proven in (Petkovšek, M., Wilf, H. and Zeilberger, D. (1996). A=B. Wellesley, MA: A K Peters. p. 160) that there is no closed form for these numbers, in terms of the sum of a fixed number of hypergeometric terms.
However, as @Robert_Israel points out, the expression could possibly be represented by different types of closed form.
edited Nov 29 at 15:03
answered Nov 28 at 18:20
Jam
4,94711431
4,94711431
2
... if "closed form" is defined as "the sum of a fixed number of hypergeometric terms". There could be other types of "closed form".
– Robert Israel
Nov 28 at 18:24
@Robert Was just thinking that. Thanks for the suggestion.
– Jam
Nov 28 at 18:26
add a comment |
2
... if "closed form" is defined as "the sum of a fixed number of hypergeometric terms". There could be other types of "closed form".
– Robert Israel
Nov 28 at 18:24
@Robert Was just thinking that. Thanks for the suggestion.
– Jam
Nov 28 at 18:26
2
2
... if "closed form" is defined as "the sum of a fixed number of hypergeometric terms". There could be other types of "closed form".
– Robert Israel
Nov 28 at 18:24
... if "closed form" is defined as "the sum of a fixed number of hypergeometric terms". There could be other types of "closed form".
– Robert Israel
Nov 28 at 18:24
@Robert Was just thinking that. Thanks for the suggestion.
– Jam
Nov 28 at 18:26
@Robert Was just thinking that. Thanks for the suggestion.
– Jam
Nov 28 at 18:26
add a comment |
The binomial coefficient for a given pair of $n geq k geq 0$ integers can be expressed in terms of a Pochhammer symbol as the following.
$$
binom n k = frac{(-1)^k(-n)_k} {k!}.
$$
The expression is valid even if $n$ is an arbitrary real number.
Here we note two things.
- The Pochhammer symbol $(-n)_k$ is zero, if $n geq 0$ and $k > -n$.
- The factorial $k!$ can be written as $(1)_k$.
Using these observations, we can express your sums in terms of a generalized hypergeometric function $_pF_q$ as the following. For the sum of the binomial coefficients, we have
$$
sum_{k=0}^n binom n k = sum_{k=0}^n frac{(-1)^k(-n)_k}{k!} = sum_{k=0}^infty (-n)_k{frac{(-1)^k}{k!}} = {_1F_0}left({{-n}atop{-}}middle|,-1right).
$$
For the sum the square of the binomial coefficients, we have
$$
sum_{k=0}^n {binom n k}^2 = sum_{k=0}^n left(frac{(-1)^k(-n)_k}{k!}right)^2 = sum_{k=0}^infty frac{left((-n)_kright)^2}{k!} cdot frac{1}{k!} = {_2F_1}left({{-n, -n}atop{1}}middle|,1right).
$$
And for the sum of the cube of the binomial coefficients $-$ also known as Franel numbers $-$, we have
$$
sum_{k=0}^n {binom n k}^3 = sum_{k=0}^n left(frac{(-1)^k(-n)_k}{k!}right)^3 = sum_{k=0}^infty frac{left((-n)_kright)^3}{(k!)^2} cdot frac{(-1)^k}{k!} = {_3F_2}left({{-n, -n, -n}atop{1, 1}}middle|,-1right).
$$
In general, for a positive integer $r$, we have the binomial sum
$$
begin{align*}
sum_{k=0}^n {binom n k}^r &= sum_{k=0}^n left(frac{(-1)^k(-n)_k}{k!}right)^r = sum_{k=0}^infty frac{left((-n)_kright)^r}{(k!)^{r-1}} cdot frac{(-1)^{rk}}{k!} \ &= {_rF_{r-1}}left({{-n, -n, dots, -n}atop{1, dots, 1}}middle|,(-1)^rright).
end{align*}
$$
add a comment |
The binomial coefficient for a given pair of $n geq k geq 0$ integers can be expressed in terms of a Pochhammer symbol as the following.
$$
binom n k = frac{(-1)^k(-n)_k} {k!}.
$$
The expression is valid even if $n$ is an arbitrary real number.
Here we note two things.
- The Pochhammer symbol $(-n)_k$ is zero, if $n geq 0$ and $k > -n$.
- The factorial $k!$ can be written as $(1)_k$.
Using these observations, we can express your sums in terms of a generalized hypergeometric function $_pF_q$ as the following. For the sum of the binomial coefficients, we have
$$
sum_{k=0}^n binom n k = sum_{k=0}^n frac{(-1)^k(-n)_k}{k!} = sum_{k=0}^infty (-n)_k{frac{(-1)^k}{k!}} = {_1F_0}left({{-n}atop{-}}middle|,-1right).
$$
For the sum the square of the binomial coefficients, we have
$$
sum_{k=0}^n {binom n k}^2 = sum_{k=0}^n left(frac{(-1)^k(-n)_k}{k!}right)^2 = sum_{k=0}^infty frac{left((-n)_kright)^2}{k!} cdot frac{1}{k!} = {_2F_1}left({{-n, -n}atop{1}}middle|,1right).
$$
And for the sum of the cube of the binomial coefficients $-$ also known as Franel numbers $-$, we have
$$
sum_{k=0}^n {binom n k}^3 = sum_{k=0}^n left(frac{(-1)^k(-n)_k}{k!}right)^3 = sum_{k=0}^infty frac{left((-n)_kright)^3}{(k!)^2} cdot frac{(-1)^k}{k!} = {_3F_2}left({{-n, -n, -n}atop{1, 1}}middle|,-1right).
$$
In general, for a positive integer $r$, we have the binomial sum
$$
begin{align*}
sum_{k=0}^n {binom n k}^r &= sum_{k=0}^n left(frac{(-1)^k(-n)_k}{k!}right)^r = sum_{k=0}^infty frac{left((-n)_kright)^r}{(k!)^{r-1}} cdot frac{(-1)^{rk}}{k!} \ &= {_rF_{r-1}}left({{-n, -n, dots, -n}atop{1, dots, 1}}middle|,(-1)^rright).
end{align*}
$$
add a comment |
The binomial coefficient for a given pair of $n geq k geq 0$ integers can be expressed in terms of a Pochhammer symbol as the following.
$$
binom n k = frac{(-1)^k(-n)_k} {k!}.
$$
The expression is valid even if $n$ is an arbitrary real number.
Here we note two things.
- The Pochhammer symbol $(-n)_k$ is zero, if $n geq 0$ and $k > -n$.
- The factorial $k!$ can be written as $(1)_k$.
Using these observations, we can express your sums in terms of a generalized hypergeometric function $_pF_q$ as the following. For the sum of the binomial coefficients, we have
$$
sum_{k=0}^n binom n k = sum_{k=0}^n frac{(-1)^k(-n)_k}{k!} = sum_{k=0}^infty (-n)_k{frac{(-1)^k}{k!}} = {_1F_0}left({{-n}atop{-}}middle|,-1right).
$$
For the sum the square of the binomial coefficients, we have
$$
sum_{k=0}^n {binom n k}^2 = sum_{k=0}^n left(frac{(-1)^k(-n)_k}{k!}right)^2 = sum_{k=0}^infty frac{left((-n)_kright)^2}{k!} cdot frac{1}{k!} = {_2F_1}left({{-n, -n}atop{1}}middle|,1right).
$$
And for the sum of the cube of the binomial coefficients $-$ also known as Franel numbers $-$, we have
$$
sum_{k=0}^n {binom n k}^3 = sum_{k=0}^n left(frac{(-1)^k(-n)_k}{k!}right)^3 = sum_{k=0}^infty frac{left((-n)_kright)^3}{(k!)^2} cdot frac{(-1)^k}{k!} = {_3F_2}left({{-n, -n, -n}atop{1, 1}}middle|,-1right).
$$
In general, for a positive integer $r$, we have the binomial sum
$$
begin{align*}
sum_{k=0}^n {binom n k}^r &= sum_{k=0}^n left(frac{(-1)^k(-n)_k}{k!}right)^r = sum_{k=0}^infty frac{left((-n)_kright)^r}{(k!)^{r-1}} cdot frac{(-1)^{rk}}{k!} \ &= {_rF_{r-1}}left({{-n, -n, dots, -n}atop{1, dots, 1}}middle|,(-1)^rright).
end{align*}
$$
The binomial coefficient for a given pair of $n geq k geq 0$ integers can be expressed in terms of a Pochhammer symbol as the following.
$$
binom n k = frac{(-1)^k(-n)_k} {k!}.
$$
The expression is valid even if $n$ is an arbitrary real number.
Here we note two things.
- The Pochhammer symbol $(-n)_k$ is zero, if $n geq 0$ and $k > -n$.
- The factorial $k!$ can be written as $(1)_k$.
Using these observations, we can express your sums in terms of a generalized hypergeometric function $_pF_q$ as the following. For the sum of the binomial coefficients, we have
$$
sum_{k=0}^n binom n k = sum_{k=0}^n frac{(-1)^k(-n)_k}{k!} = sum_{k=0}^infty (-n)_k{frac{(-1)^k}{k!}} = {_1F_0}left({{-n}atop{-}}middle|,-1right).
$$
For the sum the square of the binomial coefficients, we have
$$
sum_{k=0}^n {binom n k}^2 = sum_{k=0}^n left(frac{(-1)^k(-n)_k}{k!}right)^2 = sum_{k=0}^infty frac{left((-n)_kright)^2}{k!} cdot frac{1}{k!} = {_2F_1}left({{-n, -n}atop{1}}middle|,1right).
$$
And for the sum of the cube of the binomial coefficients $-$ also known as Franel numbers $-$, we have
$$
sum_{k=0}^n {binom n k}^3 = sum_{k=0}^n left(frac{(-1)^k(-n)_k}{k!}right)^3 = sum_{k=0}^infty frac{left((-n)_kright)^3}{(k!)^2} cdot frac{(-1)^k}{k!} = {_3F_2}left({{-n, -n, -n}atop{1, 1}}middle|,-1right).
$$
In general, for a positive integer $r$, we have the binomial sum
$$
begin{align*}
sum_{k=0}^n {binom n k}^r &= sum_{k=0}^n left(frac{(-1)^k(-n)_k}{k!}right)^r = sum_{k=0}^infty frac{left((-n)_kright)^r}{(k!)^{r-1}} cdot frac{(-1)^{rk}}{k!} \ &= {_rF_{r-1}}left({{-n, -n, dots, -n}atop{1, dots, 1}}middle|,(-1)^rright).
end{align*}
$$
edited Dec 2 at 17:21
answered Dec 2 at 15:34
user153012
6,27822277
6,27822277
add a comment |
add a comment |
Thanks for contributing an answer to Mathematics Stack Exchange!
- Please be sure to answer the question. Provide details and share your research!
But avoid …
- Asking for help, clarification, or responding to other answers.
- Making statements based on opinion; back them up with references or personal experience.
Use MathJax to format equations. MathJax reference.
To learn more, see our tips on writing great answers.
Some of your past answers have not been well-received, and you're in danger of being blocked from answering.
Please pay close attention to the following guidance:
- Please be sure to answer the question. Provide details and share your research!
But avoid …
- Asking for help, clarification, or responding to other answers.
- Making statements based on opinion; back them up with references or personal experience.
To learn more, see our tips on writing great answers.
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
StackExchange.ready(
function () {
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fmath.stackexchange.com%2fquestions%2f3017475%2fis-there-a-closed-form-for-the-sum-of-the-cubes-of-the-binomial-coefficients%23new-answer', 'question_page');
}
);
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
2
Its been proven no closed formula can exist
– Jorge Fernández
Nov 28 at 18:05
1
on a positive note, if you add $(-1)^k$ to you sum of cubes, there is closed formula called Dixon's theorem: mathworld.wolfram.com/DixonsTheorem.html
– Abdelmalek Abdesselam
Nov 28 at 18:32