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A218686 O.g.f.: Sum_{n>=0} n^n * (1+n^2*x)^n * x^n/n! * exp(-n*(1+n^2*x)*x). 3
1, 1, 2, 15, 107, 1164, 13932, 207527, 3424441, 65365273, 1366815507, 31899555046, 806153628997, 22260455705106, 659196741236329, 21028295211402871, 713819243969142111, 25836118882427921161, 988875977638287049631, 40043648314495526922945 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

COMMENTS

Compare the o.g.f. to the curious identity:

1/(1-x^2) = Sum_{n>=0} (1+n*x)^n * x^n/n! * exp(-(1+n*x)*x).

LINKS

Table of n, a(n) for n=0..19.

EXAMPLE

O.g.f: A(x) = 1 + x + 2*x^2 + 15*x^3 + 107*x^4 + 1164*x^5 + 13932*x^6 +...

where

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

simplifies to a power series in x with integer coefficients.

PROG

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

for(n=0, 30, print1(a(n), ", "))

CROSSREFS

Cf. A218684, A218687, A218685.

Sequence in context: A037556 A037492 A037572 * A279087 A037740 A037635

Adjacent sequences:  A218683 A218684 A218685 * A218687 A218688 A218689

KEYWORD

nonn

AUTHOR

Paul D. Hanna, Nov 05 2012

STATUS

approved

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Last modified September 22 14:25 EDT 2021. Contains 347607 sequences. (Running on oeis4.)