Triangle, read by rows, where T(n,k) = n!/(k!*(n-3*k)!*3^k) for n>=3*k>=0.

Terms

a(0) =1a(1) =1a(2) =1a(3) =1a(4) =2a(5) =1a(6) =8a(7) =1a(8) =20a(9) =1a(10) =40a(11) =40a(12) =1a(13) =70a(14) =280a(15) =1a(16) =112a(17) =1120a(18) =1a(19) =168a(20) =3360a(21) =2240a(22) =1a(23) =240a(24) =8400a(25) =22400a(26) =1a(27) =330a(28) =18480a(29) =123200