OFFSET
0,3
FORMULA
a(n) = [x^n] x/((1-n*x) * (1-x)^4).
a(n) = n * (6*n^(n+2) - n^5 - 3*n^4 + n^3 + n^2 - 6*n + 2)/(6 * (n-1)^4) for n > 1.
PROG
(PARI) a(n) = sum(k=1, n, binomial(k+2, 3)*n^(n-k));
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Seiichi Manyama, Dec 29 2023
STATUS
approved