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A332906
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Number of entries in the second cycles of all permutations of [n] when cycles are ordered by increasing lengths.
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3
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1, 7, 37, 241, 1661, 13301, 117209, 1150297, 12314329, 144593989, 1828734689, 24995387561, 365311053953, 5707795873261, 94637770625761, 1665132643843201, 30896642665904609, 604541044692565157, 12416248460455779089, 267500866283111679289, 6024053249628809274769
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OFFSET
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2,2
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LINKS
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FORMULA
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MAPLE
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b:= proc(n, i, t) option remember; `if`(n=0, [1, 0], `if`(i>n, 0,
add((p-> p+`if`(t>0 and t-j<1, [0, p[1]*i], 0))((i-1)!^j*
b(n-i*j, i+1, max(0, t-j))/j!*combinat[multinomial]
(n, i$j, n-i*j)), j=0..n/i)))
end:
a:= n-> b(n, 1, 2)[2]:
seq(a(n), n=2..22);
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MATHEMATICA
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multinomial[n_, k_List] := n!/Times @@ (k!);
b[n_, i_, t_] := b[n, i, t] = If[n == 0, {1, 0}, If[i>n, 0, Sum[Function[ p, p + If[p =!= 0 && t>0 && t - j < 1, {0, p[[1]]*i}, {0, 0}]][(i-1)!^j* b[n - i*j, i + 1, Max[0, t - j]]/j!*multinomial[n, Append[Array[i&, j], n - i*j]]], {j, 0, n/i}]]];
a[n_] := b[n, 1, 2][[2]];
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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