OFFSET
0,3
FORMULA
a(n) = Sum_{k=1..n} (3*n+2*k-2)!/(3*n+k-1)! * |Stirling1(n,k)|.
E.g.f.: Series_Reversion( (1 - x)^3 * (1 - exp(-x * (1 - x))) ).
PROG
(PARI) a(n) = sum(k=1, n, (3*n+2*k-2)!/(3*n+k-1)!*abs(stirling(n, k, 1)));
CROSSREFS
KEYWORD
nonn
AUTHOR
Seiichi Manyama, Sep 07 2024
STATUS
approved