OFFSET
0,3
FORMULA
a(n) = [x^n] ( (1-x)^2 * (1+x)^3 )^n.
The g.f. exp( Sum_{k>=1} a(k) * x^k/k ) has integer coefficients and equals (1/x) * Series_Reversion( x/((1-x)^2*(1+x)^3) ). See A370107.
PROG
(PARI) a(n) = sum(k=0, n, (-1)^k * binomial(2*n, k)*binomial(3*n, n-k));
CROSSREFS
KEYWORD
sign
AUTHOR
Seiichi Manyama, Feb 10 2024
STATUS
approved