OFFSET
0,2
FORMULA
a(n) = [x^n] ( (1+x)^4/(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)^3/(1+x)^4 ). See A365846.
PROG
(PARI) a(n) = sum(k=0, n, binomial(4*n, k)*binomial(4*n-k-1, n-k));
CROSSREFS
KEYWORD
nonn
AUTHOR
Seiichi Manyama, Feb 10 2024
STATUS
approved