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A122648 Expansion of e.g.f.: exp(x^2)*(exp(2*x)+1)/2. 0
1, 1, 4, 10, 44, 156, 752, 3256, 17040, 84496, 475712, 2611104, 15687872, 93376960, 594638592, 3786534784, 25412227328, 171474649344, 1206965027840, 8569374206464, 63003419470848, 468111364627456, 3582366347030528, 27733474149611520, 220255800262627328 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

LINKS

Table of n, a(n) for n=0..24.

C.-O. Chow, Counting involutory, unimodal and alternating signed permutations, Discr. Math. 306 (2006), 2222-2228.

FORMULA

a(n) ~ exp(sqrt(2*n)-n/2-1/2)*2^(n/2-3/2)*n^(n/2). - Vaclav Kotesovec, Jun 27 2013

MATHEMATICA

CoefficientList[Series[E^(x^2)*(E^(2*x)+1)/2, {x, 0, 20}], x]* Range[0, 20]! (* Vaclav Kotesovec, Jun 27 2013 *)

PROG

(PARI) my(x='x+O('x^30)); Vec(serlaplace(exp(x^2)*(exp(2*x)+1)/2))) \\ Michel Marcus, May 28 2019

CROSSREFS

Sequence in context: A149223 A149224 A149225 * A058819 A052394 A197627

Adjacent sequences:  A122645 A122646 A122647 * A122649 A122650 A122651

KEYWORD

nonn

AUTHOR

N. J. A. Sloane, Sep 22 2006

STATUS

approved

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Last modified January 19 03:54 EST 2020. Contains 331031 sequences. (Running on oeis4.)