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A218684 O.g.f.: Sum_{n>=0} (1+n^2*x)^n * x^n/n! * exp(-(1+n^2*x)*x). 3
1, 0, 1, 2, 7, 18, 96, 260, 1851, 5270, 46515, 137942, 1447202, 4433772, 53787706, 169169912, 2326986783, 7477418982, 114916173009, 375898894514, 6380455164161, 21185872231238, 393499602818322, 1323362744628080, 26691270481453228, 90755667374332324 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,4

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..25.

EXAMPLE

O.g.f: A(x) = 1 + x^2 + 2*x^3 + 7*x^4 + 18*x^5 + 96*x^6 + 260*x^7 +...

where

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

simplifies to a power series in x with integer coefficients.

PROG

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

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

CROSSREFS

Cf. A218686, A218685, A218687, A185040.

Sequence in context: A002214 A303742 A340738 * A337614 A343908 A100408

Adjacent sequences:  A218681 A218682 A218683 * A218685 A218686 A218687

KEYWORD

nonn

AUTHOR

Paul D. Hanna, Nov 05 2012

STATUS

approved

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Last modified September 23 20:42 EDT 2021. Contains 347617 sequences. (Running on oeis4.)