OFFSET
1,2
LINKS
Andrew Howroyd, Table of n, a(n) for n = 1..100
EXAMPLE
Case n=2: generators of the 5 cyclic groups are:
[ 1 0 ] [0 1] [1 0] [1 1] [0 1]
[ 0 1 ] [1 0] [1 1] [0 1] [1 1]
PROG
(GAP) Concatenation([1], List([2..10], n->Sum( Filtered( ConjugacyClassesSubgroups( SL(2, Integers mod n)), x->IsCyclic( Representative(x))), Size)));
(PARI)
MatOrder(M)={my(id=matid(#M), k=1, N=M); while(N<>id, k++; N=N*M); k}
a(n)={sum(a=0, n-1, sum(b=0, n-1, sum(c=0, n-1, sum(d=0, n-1, my(M=Mod([a, b; c, d], n)); if(matdet(M)==1, 1/eulerphi(MatOrder(M)))))))}
CROSSREFS
KEYWORD
nonn
AUTHOR
Andrew Howroyd, Jul 06 2018
STATUS
approved