OFFSET
0,6
FORMULA
a(0) = 1; a(n) = (n-1)! * Sum_{k=0..floor((n-1)/4)} (-1)^k * (4*k+1) * a(k) * a(n-1-4*k) / (k! * (n-1-4*k)!).
PROG
(PARI) a_vector(n) = my(v=vector(n+1)); v[1]=1; for(i=1, n, v[i+1]=(i-1)!*sum(j=0, (i-1)\4, (-1)^j*(4*j+1)*v[j+1]*v[i-4*j]/(j!*(i-1-4*j)!))); v;
CROSSREFS
KEYWORD
sign
AUTHOR
Seiichi Manyama, Nov 28 2023
STATUS
approved