Triangle read by rows: T(n, k) = binomial(3*n, k-1) + binomial(3*n, n-k).

Terms

a(0) =2a(1) =7a(2) =7a(3) =37a(4) =18a(5) =37a(6) =221a(7) =78a(8) =78a(9) =221a(10) =1366a(11) =470a(12) =210a(13) =470a(14) =1366a(15) =8569a(16) =3078a(17) =969a(18) =969a(19) =3078a(20) =8569a(21) =54265a(22) =20370a(23) =6195a(24) =2660a(25) =6195a(26) =20370a(27) =54265a(28) =346105a(29) =134620