Is there a closed form for the sum of the cubes of the binomial coefficients?












7














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 $alpha in mathbb{N}_0$?










share|cite|improve this question




















  • 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
















7














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 $alpha in mathbb{N}_0$?










share|cite|improve this question




















  • 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














7












7








7


3





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 $alpha in mathbb{N}_0$?










share|cite|improve this question















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






share|cite|improve this question















share|cite|improve this question













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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














  • 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










2 Answers
2






active

oldest

votes


















6














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.






share|cite|improve this answer



















  • 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



















1














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.





  1. The Pochhammer symbol $(-n)_k$ is zero, if $n geq 0$ and $k > -n$.

  2. 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




$$
begin{align*}
sum_{k=0}^n {binom n k}^r &= sum_{k=0}^n left(frac{(-1)^k(-n)_k}{k!}right)^r = sum_{k=0}^infty frac{left((-n)_kright)^r}{(k!)^{r-1}} cdot frac{(-1)^{rk}}{k!} \ &= {_rF_{r-1}}left({{-n, -n, dots, -n}atop{1, dots, 1}}middle|,(-1)^rright).
end{align*}
$$







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    2 Answers
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    2 Answers
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    active

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    6














    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.






    share|cite|improve this answer



















    • 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
















    6














    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.






    share|cite|improve this answer



















    • 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














    6












    6








    6






    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.






    share|cite|improve this answer














    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.







    share|cite|improve this answer














    share|cite|improve this answer



    share|cite|improve this answer








    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














    • 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











    1














    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.





    1. The Pochhammer symbol $(-n)_k$ is zero, if $n geq 0$ and $k > -n$.

    2. 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




    $$
    begin{align*}
    sum_{k=0}^n {binom n k}^r &= sum_{k=0}^n left(frac{(-1)^k(-n)_k}{k!}right)^r = sum_{k=0}^infty frac{left((-n)_kright)^r}{(k!)^{r-1}} cdot frac{(-1)^{rk}}{k!} \ &= {_rF_{r-1}}left({{-n, -n, dots, -n}atop{1, dots, 1}}middle|,(-1)^rright).
    end{align*}
    $$







    share|cite|improve this answer




























      1














      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.





      1. The Pochhammer symbol $(-n)_k$ is zero, if $n geq 0$ and $k > -n$.

      2. 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




      $$
      begin{align*}
      sum_{k=0}^n {binom n k}^r &= sum_{k=0}^n left(frac{(-1)^k(-n)_k}{k!}right)^r = sum_{k=0}^infty frac{left((-n)_kright)^r}{(k!)^{r-1}} cdot frac{(-1)^{rk}}{k!} \ &= {_rF_{r-1}}left({{-n, -n, dots, -n}atop{1, dots, 1}}middle|,(-1)^rright).
      end{align*}
      $$







      share|cite|improve this answer


























        1












        1








        1






        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.





        1. The Pochhammer symbol $(-n)_k$ is zero, if $n geq 0$ and $k > -n$.

        2. 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




        $$
        begin{align*}
        sum_{k=0}^n {binom n k}^r &= sum_{k=0}^n left(frac{(-1)^k(-n)_k}{k!}right)^r = sum_{k=0}^infty frac{left((-n)_kright)^r}{(k!)^{r-1}} cdot frac{(-1)^{rk}}{k!} \ &= {_rF_{r-1}}left({{-n, -n, dots, -n}atop{1, dots, 1}}middle|,(-1)^rright).
        end{align*}
        $$







        share|cite|improve this answer














        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.





        1. The Pochhammer symbol $(-n)_k$ is zero, if $n geq 0$ and $k > -n$.

        2. 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




        $$
        begin{align*}
        sum_{k=0}^n {binom n k}^r &= sum_{k=0}^n left(frac{(-1)^k(-n)_k}{k!}right)^r = sum_{k=0}^infty frac{left((-n)_kright)^r}{(k!)^{r-1}} cdot frac{(-1)^{rk}}{k!} \ &= {_rF_{r-1}}left({{-n, -n, dots, -n}atop{1, dots, 1}}middle|,(-1)^rright).
        end{align*}
        $$








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        edited Dec 2 at 17:21

























        answered Dec 2 at 15:34









        user153012

        6,27822277




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