a(n) = (2/3) * 4^n * binomial(3*n, n).

A036909

a(n) = (2/3) * 4^n * binomial(3*n, n).

Terms

    a(0) =8a(1) =160a(2) =3584a(3) =84480a(4) =2050048a(5) =50692096a(6) =1270087680a(7) =32133218304a(8) =819082035200

External references