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A339428
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Triangle read by rows: T(n,k) is the number of connected functions on n points with a loop of length k.
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15
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1, 1, 1, 2, 1, 1, 4, 3, 1, 1, 9, 6, 3, 1, 1, 20, 16, 9, 4, 1, 1, 48, 37, 23, 11, 4, 1, 1, 115, 96, 62, 35, 14, 5, 1, 1, 286, 239, 169, 97, 46, 18, 5, 1, 1, 719, 622, 451, 282, 145, 63, 21, 6, 1, 1, 1842, 1607, 1217, 792, 440, 206, 80, 25, 6, 1, 1
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OFFSET
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1,4
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LINKS
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FORMULA
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G.f. of k-th column: (1/k)*Sum_{d|k} phi(d) * r(x^d)^(k/d) where r(x) is the g.f. of A000081.
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EXAMPLE
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Triangle begins:
1;
1, 1;
2, 1, 1;
4, 3, 1, 1;
9, 6, 3, 1, 1;
20, 16, 9, 4, 1, 1;
48, 37, 23, 11, 4, 1, 1;
115, 96, 62, 35, 14, 5, 1, 1;
286, 239, 169, 97, 46, 18, 5, 1, 1;
719, 622, 451, 282, 145, 63, 21, 6, 1, 1;
...
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PROG
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(PARI) \\ TreeGf is A000081 as g.f.
TreeGf(N) = {my(A=vector(N, j, 1)); for (n=1, N-1, A[n+1] = 1/n * sum(k=1, n, sumdiv(k, d, d*A[d]) * A[n-k+1] ) ); x*Ser(A)}
ColSeq(n, k)={my(r=TreeGf(max(0, n+1-k))); Vec(sumdiv(k, d, eulerphi(d)*subst(r + O(x*x^(n\d)), x, x^d)^(k/d))/k, -n)}
M(n, m=n)=Mat(vector(m, k, ColSeq(n, k)~))
{ my(T=M(12)); for(n=1, #T~, print(T[n, 1..n])) }
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CROSSREFS
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Columns 1..12 are A000081, A027852, A029852, A029853, A029868, A029869, A029870, A029871, A032205, A032206, A032207, A032208.
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KEYWORD
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AUTHOR
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STATUS
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approved
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