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A290354
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a(n) is the n-th term of the n-th Euler transform of the sequence with g.f. 1+x.
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5
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1, 1, 2, 6, 30, 170, 1337, 12166, 133476, 1676364, 23970089, 383172262, 6783362586, 131697494825, 2783238819896, 63605879539200, 1563127601683456, 41107799958703376, 1151957989511106438, 34268629198432285436, 1078577860182473404134, 35809701458658690462644
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OFFSET
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0,3
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COMMENTS
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a(n) is also the number of unlabeled rooted trees with exactly n leaves, all in level n. a(3) = 6:
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LINKS
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B. A. Huberman and T. Hogg, Complexity and adaptation, Evolution, games and learning (Los Alamos, N.M., 1985). Phys. D 22 (1986), no. 1-3, 376-384.
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FORMULA
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Conjecture: a(n) ~ c * 2^n * n^(n-4/3) / Pi^n, where c = 4.4923... - Vaclav Kotesovec, Aug 14 2017
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MAPLE
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with(numtheory):
b:= proc(n, k) option remember; `if`(n<2, 1, `if`(k=0, 0, add(
add(b(d, k-1)*d, d=divisors(j))*b(n-j, k), j=1..n)/n))
end:
a:= n-> b(n$2):
seq(a(n), n=0..25);
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MATHEMATICA
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b[n_, k_]:=b[n, k]=If[n<2, 1, If[k==0, 0, Sum[Sum[b[d, k - 1]*d, {d, Divisors[j]}] b[n - j, k], {j, n}]/n]]; Table[b[n, n], {n, 0, 30}] (* Indranil Ghosh, Jul 30 2017, after Maple code *)
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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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