OFFSET
0,3
FORMULA
a(n) = [x^n] n*x /((1-x) * (1-n*x)^4).
a(n) = n * (n^n * (n^6-7*n^4+5*n^3+12*n^2-11*n-6) + 6)/(6 * (n-1)^4) for n > 1.
PROG
(PARI) a(n) = sum(k=1, n, binomial(k+2, 3)*n^k);
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Seiichi Manyama, Dec 29 2023
STATUS
approved