OFFSET
0,5
FORMULA
a(0) = 1; a(n) = Sum_{k=1..n} binomial(n-1,k-1) * Stirling1(k,3) * a(n-k).
a(n) = Sum_{k=0..floor(n/3)} (3*k)! * Stirling1(n,3*k)/(6^k * k!).
PROG
(PARI) my(N=30, x='x+O('x^N)); Vec(serlaplace(exp(log(1+x)^3/6)))
(PARI) a_vector(n) = my(v=vector(n+1)); v[1]=1; for(i=1, n, v[i+1]=sum(j=1, i, binomial(i-1, j-1)*stirling(j, 3, 1)*v[i-j+1])); v;
(PARI) a(n) = sum(k=0, n\3, (3*k)!*stirling(n, 3*k, 1)/(6^k*k!));
CROSSREFS
KEYWORD
sign
AUTHOR
Seiichi Manyama, May 18 2022
STATUS
approved