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