a(n) = [x^(3*n)] ( (1 + x)/(1 - x) )^n.

A333715

a(n) = [x^(3*n)] ( (1 + x)/(1 - x) )^n.

Terms

    a(0) =1a(1) =2a(2) =24a(3) =326a(4) =4672a(5) =69002a(6) =1038984a(7) =15856206a(8) =244396544a(9) =3795731282a(10) =59307908024a(11) =931222155030

External references