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A009252 E.g.f. exp(x*tan(x)) (even powers only). 0
1, 2, 20, 456, 18192, 1111840, 96035136, 11101474944, 1651123634432, 306656507699712, 69472549405824000, 18838618322988648448, 6019938761233443262464, 2237523930630521828745216 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

LINKS

Table of n, a(n) for n=0..13.

FORMULA

a(n)=sum(k=1..n, (binomial(2*n,k)*sum(j=k..2*n-k, binomial(j-1,k-1)*j!*(-1)^(n+j)*2^(2*n-k-j)*stirling2(2*n-k,j)))), n>0, a(0)=1. [Vladimir Kruchinin, Jun 06 2011]

MATHEMATICA

Exp[ Tan[ x ]*x ] (* Even Part *)

PROG

(Maxima)

a(n):=sum((binomial(2*n, k)*sum(binomial(j-1, k-1)*j!*(-1)^(n+j)*2^(2*n-k-j)*stirling2(2*n-k, j), j, k, 2*n-k)), k, 1, n); [Vladimir Kruchinin, Jun 06 2011]

CROSSREFS

Sequence in context: A012533 A009160 A188811 * A210901 A012816 A012340

Adjacent sequences:  A009249 A009250 A009251 * A009253 A009254 A009255

KEYWORD

nonn

AUTHOR

R. H. Hardin

EXTENSIONS

Extended and signs tested Mar 15 1997 by Olivier Gérard.

STATUS

approved

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Last modified July 25 00:22 EDT 2014. Contains 244897 sequences.