Proper condition on the dihedral group












1














Is there a theream which is a condition on $ninmathbb N$ that says when the dihedral group, $D_{n}$, has non-cyclic subgroups?



After spending some time figuring a condition I tried to find some similar thread but didn't find any.










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  • 1




    When $n$ is composite.
    – user10354138
    Dec 1 '18 at 13:22
















1














Is there a theream which is a condition on $ninmathbb N$ that says when the dihedral group, $D_{n}$, has non-cyclic subgroups?



After spending some time figuring a condition I tried to find some similar thread but didn't find any.










share|cite|improve this question




















  • 1




    When $n$ is composite.
    – user10354138
    Dec 1 '18 at 13:22














1












1








1


3





Is there a theream which is a condition on $ninmathbb N$ that says when the dihedral group, $D_{n}$, has non-cyclic subgroups?



After spending some time figuring a condition I tried to find some similar thread but didn't find any.










share|cite|improve this question















Is there a theream which is a condition on $ninmathbb N$ that says when the dihedral group, $D_{n}$, has non-cyclic subgroups?



After spending some time figuring a condition I tried to find some similar thread but didn't find any.







group-theory dihedral-groups






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edited Dec 1 '18 at 13:38









Jean-Claude Arbaut

14.7k63464




14.7k63464










asked Dec 1 '18 at 13:07









vesii

685




685








  • 1




    When $n$ is composite.
    – user10354138
    Dec 1 '18 at 13:22














  • 1




    When $n$ is composite.
    – user10354138
    Dec 1 '18 at 13:22








1




1




When $n$ is composite.
– user10354138
Dec 1 '18 at 13:22




When $n$ is composite.
– user10354138
Dec 1 '18 at 13:22










2 Answers
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oldest

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2














Dihedral group $D_n = <r, s | r^n = s^2 = 1, rs = sr^{-1}>, forall n ge3$.



By your question, $D_n le D_n$. So true for $forall nge3$.



But if we want a proper non-cyclic subgroup, then we have to consider some $<r^a,s>$.
Hence when $n$ is composite we get a required subgroup.






share|cite|improve this answer





























    1














    Any cyclic group has unique subgroup of any order which is divisior of its order



    Now in $D_n$ How many subgroup of order 2?



    They are at least n .



    SO for n>1






    share|cite|improve this answer





















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      2 Answers
      2






      active

      oldest

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      2 Answers
      2






      active

      oldest

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      active

      oldest

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      2














      Dihedral group $D_n = <r, s | r^n = s^2 = 1, rs = sr^{-1}>, forall n ge3$.



      By your question, $D_n le D_n$. So true for $forall nge3$.



      But if we want a proper non-cyclic subgroup, then we have to consider some $<r^a,s>$.
      Hence when $n$ is composite we get a required subgroup.






      share|cite|improve this answer


























        2














        Dihedral group $D_n = <r, s | r^n = s^2 = 1, rs = sr^{-1}>, forall n ge3$.



        By your question, $D_n le D_n$. So true for $forall nge3$.



        But if we want a proper non-cyclic subgroup, then we have to consider some $<r^a,s>$.
        Hence when $n$ is composite we get a required subgroup.






        share|cite|improve this answer
























          2












          2








          2






          Dihedral group $D_n = <r, s | r^n = s^2 = 1, rs = sr^{-1}>, forall n ge3$.



          By your question, $D_n le D_n$. So true for $forall nge3$.



          But if we want a proper non-cyclic subgroup, then we have to consider some $<r^a,s>$.
          Hence when $n$ is composite we get a required subgroup.






          share|cite|improve this answer












          Dihedral group $D_n = <r, s | r^n = s^2 = 1, rs = sr^{-1}>, forall n ge3$.



          By your question, $D_n le D_n$. So true for $forall nge3$.



          But if we want a proper non-cyclic subgroup, then we have to consider some $<r^a,s>$.
          Hence when $n$ is composite we get a required subgroup.







          share|cite|improve this answer












          share|cite|improve this answer



          share|cite|improve this answer










          answered Dec 1 '18 at 13:37









          Offlaw

          2649




          2649























              1














              Any cyclic group has unique subgroup of any order which is divisior of its order



              Now in $D_n$ How many subgroup of order 2?



              They are at least n .



              SO for n>1






              share|cite|improve this answer


























                1














                Any cyclic group has unique subgroup of any order which is divisior of its order



                Now in $D_n$ How many subgroup of order 2?



                They are at least n .



                SO for n>1






                share|cite|improve this answer
























                  1












                  1








                  1






                  Any cyclic group has unique subgroup of any order which is divisior of its order



                  Now in $D_n$ How many subgroup of order 2?



                  They are at least n .



                  SO for n>1






                  share|cite|improve this answer












                  Any cyclic group has unique subgroup of any order which is divisior of its order



                  Now in $D_n$ How many subgroup of order 2?



                  They are at least n .



                  SO for n>1







                  share|cite|improve this answer












                  share|cite|improve this answer



                  share|cite|improve this answer










                  answered Dec 1 '18 at 14:04









                  Shubham

                  1,5851519




                  1,5851519






























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