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 A316564 Triangle read by rows: T(n,k) is the number of elements of the group SL(2, Z(n)) with order k, 1 <= k <= A316563(n). 7
 1, 1, 3, 2, 1, 1, 8, 6, 0, 8, 1, 7, 8, 24, 0, 8, 1, 1, 20, 30, 24, 20, 0, 0, 0, 24, 1, 7, 26, 24, 0, 74, 0, 0, 0, 0, 0, 12, 1, 1, 56, 42, 0, 56, 48, 84, 0, 0, 0, 0, 0, 48, 1, 15, 32, 144, 0, 96, 0, 96, 1, 1, 98, 54, 0, 98, 0, 0, 144, 0, 0, 108, 0, 0, 0, 0, 0, 144 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 COMMENTS For coprime p,q the group SL(p*q, Z(n)) is isomorphic to the direct product of the two groups SL(p, Z(n)) and SL(q, Z(n)). LINKS Andrew Howroyd, Table of n, a(n) for n = 1..3478 (first 60 rows) FORMULA T(p*q,k) = Sum_{i>0, j>0, k=lcm(i, j)} T(p, i)*T(q, j) for gcd(p, q)=1. T(n,k) = Sum_{d|k} mu(d/k) A316586(n,d). EXAMPLE Triangle begins:   1;   1,  3,  2;   1,  1,  8, 6, 0, 8;   1,  7,  8, 24, 0, 8;   1,  1, 20, 30, 24, 20, 0, 0, 0, 24;   1,  7, 26, 24, 0, 74, 0, 0, 0, 0, 0, 12;   1,  1, 56, 42, 0, 56, 48, 84, 0, 0, 0, 0, 0, 48;   1, 15, 32, 144, 0, 96, 0, 96;   1,  1, 98, 54, 0, 98, 0, 0, 144, 0, 0, 108, 0, 0, 0, 0, 0, 144;   ... PROG (PARI) MatOrder(M)={my(id=matid(#M), k=1, N=M); while(N<>id, k++; N=N*M); k} row(n)={my(L=List()); for(a=0, n-1, for(b=0, n-1, for(c=0, n-1, for(d=0, n-1, my(M=Mod([a, b; c, d], n)); if(matdet(M)==1, my(t=MatOrder(M)); while(#L

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Last modified January 20 23:16 EST 2020. Contains 331104 sequences. (Running on oeis4.)