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A054363
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Number of unlabeled 5-ary cacti having n polygons.
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4
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1, 1, 5, 15, 85, 510, 4051, 33130, 291925, 2661255, 25059670, 241724380, 2379912355, 23833198140, 242173108050, 2491817151160, 25921371278805, 272256630756265, 2884054952424115, 30784716141936525, 330853932861650870, 3577823885433087690, 38907658120970944700
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OFFSET
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0,3
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LINKS
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Andrew Howroyd, Table of n, a(n) for n = 0..200
Miklos Bona, Michel Bousquet, Gilbert Labelle and Pierre Leroux, Enumeration of m-ary cacti, Advances in Applied Mathematics, 24 (2000), 22-56 (pdf, dvi).
Index entries for sequences related to cacti
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FORMULA
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a(n) = (1/n)*(Sum_{d|n} phi(n/d)*binomial(5*d, d)) - 4*binomial(5*n, n)/(4*n+1) for n > 0. - Andrew Howroyd, May 02 2018
a(n) ~ 5^(5*n + 1/2) / (sqrt(Pi) * n^(5/2) * 2^(8*n + 7/2)). - Vaclav Kotesovec, Jul 17 2017
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MATHEMATICA
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a[n_] := If[n == 0, 1, (Binomial[5*n, n]/(4*n + 1) + DivisorSum[n, Binomial[5*#, #]*EulerPhi[n/#]*Boole[# < n] & ])/n]; Table[a[n], {n, 0, 24}] (* Jean-François Alcover, Jul 17 2017 *)
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PROG
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(PARI) a(n) = if(n==0, 1, sumdiv(n, d, eulerphi(n/d)*binomial(5*d, d))/n - 4*binomial(5*n, n)/(4*n+1)) \\ Andrew Howroyd, May 02 2018
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CROSSREFS
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Column k=5 of A303912.
Cf. A054364, A054365.
Sequence in context: A165470 A165625 A058820 * A211944 A336998 A276474
Adjacent sequences: A054360 A054361 A054362 * A054364 A054365 A054366
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KEYWORD
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nonn
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AUTHOR
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Simon Plouffe
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EXTENSIONS
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More terms from Jean-François Alcover, Jul 17 2017
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STATUS
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approved
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