OFFSET
0,3
LINKS
Harvey P. Dale, Table of n, a(n) for n = 0..600
FORMULA
E.g.f.: exp(x+x^2/2+x^4/24).
a(n) = n!*sum(k=1..n, sum(j=floor((4*k-n)/3)..floor((4*k-n)/2), binomial(j,n-4*k+3*j)*12^(j-k)*binomial(k,j)*2^(-n+3*k-2*j))/k!), n>0, a(0)=1.
Recurrence: 6*a(n) = 6*a(n-1) + 6*(n-1)*a(n-2) + (n-3)*(n-2)*(n-1)*a(n-4). - Vaclav Kotesovec, Oct 09 2013
a(n) ~ 1/2*exp((6*n)^(1/4) + sqrt(6*n)/2 - 3*n/4 - 3/4) * n^(3*n/4) * 6^(-n/4) * (1 + 3^(5/4)/(16*(2*n)^(3/4)) + 7*sqrt(3/2)/(8*sqrt(n)) - 3^(3/4)/(2*(2*n)^(1/4))). - Vaclav Kotesovec, Oct 09 2013
MATHEMATICA
With[{nn=30}, CoefficientList[Series[Exp[x+x^2/2+x^4/24], {x, 0, nn}], x]Range[0, nn]!] (* Harvey P. Dale, Jun 21 2012 *)
PROG
(Maxima)
a(n):=n!*sum(sum(binomial(j, n-4*k+3*j)*12^(j-k)*binomial(k, j)*2^(-n+3*k-2*j), j, floor((4*k-n)/3), floor((4*k-n)/2))/k!, k, 1, n);
(PARI)
N=33; x='x+O('x^N);
egf=exp(x+x^2/2+x^4/4!);
Vec(serlaplace(egf))
/* Joerg Arndt, Sep 15 2012 */
CROSSREFS
KEYWORD
nonn
AUTHOR
Vladimir Kruchinin, May 24 2011
EXTENSIONS
More terms from Harvey P. Dale, Jun 21 2012
STATUS
approved