a(n) = (1/7) * Sum_{k=0..n-1} binomial(7*n,7*k+2).

A387749

a(n) = (1/7) * Sum_{k=0..n-1} binomial(7*n,7*k+2).

Terms

    a(0) =0a(1) =3a(2) =299a(3) =44927a(4) =5346759a(5) =709330491a(6) =89255698947

External references