OFFSET
0,4
FORMULA
a(0) = 1; a(n) = -(n-1)!/2 * Sum_{k=3..n} (-1)^k * k/(k-2) * a(n-k)/(n-k)!.
a(n) = n! * Sum_{k=0..floor(n/3)} Stirling1(n-2*k,k)/(2^k * (n-2*k)!).
PROG
(PARI) my(N=30, x='x+O('x^N)); Vec(serlaplace((1+x)^(x^2/2)))
(PARI) my(N=30, x='x+O('x^N)); Vec(serlaplace(exp(x^2/2*log(1+x))))
(PARI) a_vector(n) = my(v=vector(n+1)); v[1]=1; for(i=1, n, v[i+1]=-(i-1)!/2*sum(j=3, i, (-1)^j*j/(j-2)*v[i-j+1]/(i-j)!)); v;
(PARI) a(n) = n!*sum(k=0, n\3, stirling(n-2*k, k, 1)/(2^k*(n-2*k)!));
CROSSREFS
KEYWORD
sign
AUTHOR
Seiichi Manyama, Jul 09 2022
STATUS
approved