OFFSET
0,4
FORMULA
a(n) = (n!/(2*n+1)!) * Sum_{k=0..floor(n/3)} (2*n+k)! * |Stirling1(n-2*k,k)|/(n-2*k)!.
PROG
(PARI) a(n) = n!*sum(k=0, n\3, (2*n+k)!*abs(stirling(n-2*k, k, 1))/(n-2*k)!)/(2*n+1)!;
CROSSREFS
KEYWORD
nonn
AUTHOR
Seiichi Manyama, Mar 15 2024
STATUS
approved