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A221094 O.g.f.: Sum_{n>=0} n!^2 * x^n / Product_{k=1..n} (1 + k*(n-k+1)*x). 0
1, 1, 3, 21, 263, 5165, 146335, 5649397, 285069735, 18214525629, 1437313035887, 137272113393413, 15605422414146487, 2082375903282194893, 322303158660868063359, 57271523430269553109269, 11579903781095519639058119, 2643368434346324374530280157, 676521525314300179793917303951 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

COMMENTS

Compare to: Sum_{n>=0} n!^2 * x^n / Product_{k=1..n} (1 + k^2*x) = Sum_{n>=0}  A110501(n)*x^n, where A110501 is unsigned Genocchi numbers of even index.

LINKS

Table of n, a(n) for n=0..18.

EXAMPLE

G.f.: A(x) = 1 + x + 3*x^2 + 21*x^3 + 263*x^4 + 5165*x^5 + 146335*x^6 +...

where

A(x) = 1 + x/(1+x) + 2!^2*x^2/((1+1*2*x)*(1+2*1*x)) + 3!^2*x^3/((1+1*3*x)*(1+2*2*x)*(1+3*1*x)) + 4!^2*x^4/((1+1*4*x)*(1+2*3*x)*(1+3*2*x)*(1+4*1*x)) + 5!^2*x^5/((1+1*5*x)*(1+2*4*x)*(1+3*3*x)*(1+4*2*x)*(1+5*1*x)) +...

MATHEMATICA

CoefficientList[Series[Sum[(n!)^2 x^n/Product[1+k(n-k+1)x, {k, n}], {n, 0, 20}], {x, 0, 20}], x] (* Harvey P. Dale, Aug 03 2020 *)

PROG

(PARI) {a(n)=polcoeff(sum(m=0, n, m!^2*x^m/prod(k=1, m, 1+(m-k+1)*k*x+x*O(x^n))), n)}

for(n=0, 20, print1(a(n), ", "))

CROSSREFS

Sequence in context: A265002 A012131 A322224 * A098278 A269938 A277454

Adjacent sequences:  A221091 A221092 A221093 * A221095 A221096 A221097

KEYWORD

nonn

AUTHOR

Paul D. Hanna, Jan 03 2013

STATUS

approved

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Last modified December 7 15:24 EST 2021. Contains 349581 sequences. (Running on oeis4.)