a(n) = (3^n/n!^2) * Product_{k=1..n} (6k-4)*(6k-5).

A184424

a(n) = (3^n/n!^2) * Product_{k=1..n} (6k-4)*(6k-5).

Terms

    a(0) =1a(1) =6a(2) =252a(3) =15288a(4) =1089270a(5) =84963060a(6) =7023612960a(7) =604604070720

External references