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A052809
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A simple grammar: number of cycles of cycles.
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3
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0, 0, 2, 6, 28, 175, 1368, 12838, 140656, 1762794, 24878320, 390495336, 6748280064, 127324033824, 2604355096224, 57404425654080, 1356401049662208, 34202807058719568, 916723959720053760
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OFFSET
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0,3
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LINKS
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FORMULA
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E.g.f.: log(-1/(-1+log(-1/(-1+x))))*x.
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MAPLE
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spec := [S, {B=Cycle(C), C=Cycle(Z), S=Prod(B, Z)}, labeled]: seq(combstruct[count](spec, size=n), n=0..20);
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MATHEMATICA
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CoefficientList[Series[-Log[1+Log[1-x]]*x, {x, 0, 20}], x]* Range[0, 20]! (* Vaclav Kotesovec, Oct 01 2013 *)
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PROG
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(PARI) a(n) = n*sum(k=1, n-1, (k-1)!*abs(stirling(n-1, k, 1))); \\ Seiichi Manyama, May 20 2022
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CROSSREFS
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KEYWORD
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easy,nonn
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AUTHOR
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encyclopedia(AT)pommard.inria.fr, Jan 25 2000
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STATUS
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approved
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