OFFSET
0,6
FORMULA
a(0) = 1; a(n) = (n-1)! * Sum_{k=5..n} k/(k-4) * a(n-k)/(n-k)!.
a(n) = n! * Sum_{k=0..floor(n/5)} |Stirling1(n-4*k,k)|/(n-4*k)!.
a(n) ~ n! * (1 - 4/n - 16*log(n)/n^2). - Vaclav Kotesovec, Jul 21 2022
PROG
(PARI) my(N=30, x='x+O('x^N)); Vec(serlaplace((1-x)^(-x^4)))
(PARI) my(N=30, x='x+O('x^N)); Vec(serlaplace(exp(-x^4*log(1-x))))
(PARI) a_vector(n) = my(v=vector(n+1)); v[1]=1; for(i=1, n, v[i+1]=(i-1)!*sum(j=5, i, j/(j-4)*v[i-j+1]/(i-j)!)); v;
(PARI) a(n) = n!*sum(k=0, n\5, abs(stirling(n-4*k, k, 1))/(n-4*k)!);
CROSSREFS
KEYWORD
nonn
AUTHOR
Seiichi Manyama, Jul 09 2022
STATUS
approved