The use of euler function to calculate the order of an element











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Just trying to check if I understand the material right. I would like to calculate $o(5)$ for $U_6$ (or $mathbb{Z}_6^times$). On one hand I think that we need to use the euler function to do so. But on the other hand we have the following theorem:
$$o(a)=min{ninmathbb{N}|a^n=e}$$
So as I understand, I need to find all the minimal $ninmathbb{N}$ so $5^n=1$ (although I'm not sure that $e=1$). From my previous thread I learned that $5^n=5+...+5,(mod,6)$. But there is no $ninmathbb{N}$ so $5^n=1$.



Also what will happen with bigger numbers? For example how to calculate $o(5)$ for $U_{27}$?










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    up vote
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    down vote

    favorite












    Just trying to check if I understand the material right. I would like to calculate $o(5)$ for $U_6$ (or $mathbb{Z}_6^times$). On one hand I think that we need to use the euler function to do so. But on the other hand we have the following theorem:
    $$o(a)=min{ninmathbb{N}|a^n=e}$$
    So as I understand, I need to find all the minimal $ninmathbb{N}$ so $5^n=1$ (although I'm not sure that $e=1$). From my previous thread I learned that $5^n=5+...+5,(mod,6)$. But there is no $ninmathbb{N}$ so $5^n=1$.



    Also what will happen with bigger numbers? For example how to calculate $o(5)$ for $U_{27}$?










    share|cite|improve this question
























      up vote
      0
      down vote

      favorite









      up vote
      0
      down vote

      favorite











      Just trying to check if I understand the material right. I would like to calculate $o(5)$ for $U_6$ (or $mathbb{Z}_6^times$). On one hand I think that we need to use the euler function to do so. But on the other hand we have the following theorem:
      $$o(a)=min{ninmathbb{N}|a^n=e}$$
      So as I understand, I need to find all the minimal $ninmathbb{N}$ so $5^n=1$ (although I'm not sure that $e=1$). From my previous thread I learned that $5^n=5+...+5,(mod,6)$. But there is no $ninmathbb{N}$ so $5^n=1$.



      Also what will happen with bigger numbers? For example how to calculate $o(5)$ for $U_{27}$?










      share|cite|improve this question













      Just trying to check if I understand the material right. I would like to calculate $o(5)$ for $U_6$ (or $mathbb{Z}_6^times$). On one hand I think that we need to use the euler function to do so. But on the other hand we have the following theorem:
      $$o(a)=min{ninmathbb{N}|a^n=e}$$
      So as I understand, I need to find all the minimal $ninmathbb{N}$ so $5^n=1$ (although I'm not sure that $e=1$). From my previous thread I learned that $5^n=5+...+5,(mod,6)$. But there is no $ninmathbb{N}$ so $5^n=1$.



      Also what will happen with bigger numbers? For example how to calculate $o(5)$ for $U_{27}$?







      group-theory






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      asked 2 days ago









      vesii

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      475






















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          $5^n$ means repeating the group operation on $5$ $n$ times. Since we're dealing with the multiplicative group here, the group operation is multiplication, not addition.






          share|cite|improve this answer





















          • Thanks for the fast replay. Although there is still no solution for $5^n=1$ right?
            – vesii
            2 days ago












          • @vesii There is. $5^2=25=1$ mod6
            – Y. Forman
            2 days ago










          • oh right! and how the euler equation comes in handy? can we calculate all of the numbers?
            – vesii
            2 days ago













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          1 Answer
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          1 Answer
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          active

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          up vote
          0
          down vote













          $5^n$ means repeating the group operation on $5$ $n$ times. Since we're dealing with the multiplicative group here, the group operation is multiplication, not addition.






          share|cite|improve this answer





















          • Thanks for the fast replay. Although there is still no solution for $5^n=1$ right?
            – vesii
            2 days ago












          • @vesii There is. $5^2=25=1$ mod6
            – Y. Forman
            2 days ago










          • oh right! and how the euler equation comes in handy? can we calculate all of the numbers?
            – vesii
            2 days ago

















          up vote
          0
          down vote













          $5^n$ means repeating the group operation on $5$ $n$ times. Since we're dealing with the multiplicative group here, the group operation is multiplication, not addition.






          share|cite|improve this answer





















          • Thanks for the fast replay. Although there is still no solution for $5^n=1$ right?
            – vesii
            2 days ago












          • @vesii There is. $5^2=25=1$ mod6
            – Y. Forman
            2 days ago










          • oh right! and how the euler equation comes in handy? can we calculate all of the numbers?
            – vesii
            2 days ago















          up vote
          0
          down vote










          up vote
          0
          down vote









          $5^n$ means repeating the group operation on $5$ $n$ times. Since we're dealing with the multiplicative group here, the group operation is multiplication, not addition.






          share|cite|improve this answer












          $5^n$ means repeating the group operation on $5$ $n$ times. Since we're dealing with the multiplicative group here, the group operation is multiplication, not addition.







          share|cite|improve this answer












          share|cite|improve this answer



          share|cite|improve this answer










          answered 2 days ago









          Y. Forman

          11.3k423




          11.3k423












          • Thanks for the fast replay. Although there is still no solution for $5^n=1$ right?
            – vesii
            2 days ago












          • @vesii There is. $5^2=25=1$ mod6
            – Y. Forman
            2 days ago










          • oh right! and how the euler equation comes in handy? can we calculate all of the numbers?
            – vesii
            2 days ago




















          • Thanks for the fast replay. Although there is still no solution for $5^n=1$ right?
            – vesii
            2 days ago












          • @vesii There is. $5^2=25=1$ mod6
            – Y. Forman
            2 days ago










          • oh right! and how the euler equation comes in handy? can we calculate all of the numbers?
            – vesii
            2 days ago


















          Thanks for the fast replay. Although there is still no solution for $5^n=1$ right?
          – vesii
          2 days ago






          Thanks for the fast replay. Although there is still no solution for $5^n=1$ right?
          – vesii
          2 days ago














          @vesii There is. $5^2=25=1$ mod6
          – Y. Forman
          2 days ago




          @vesii There is. $5^2=25=1$ mod6
          – Y. Forman
          2 days ago












          oh right! and how the euler equation comes in handy? can we calculate all of the numbers?
          – vesii
          2 days ago






          oh right! and how the euler equation comes in handy? can we calculate all of the numbers?
          – vesii
          2 days ago




















           

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