Triangle T(n,k) = binomial(3*n+1, 2*n+k+1), read by rows.

Terms

a(0) =1a(1) =4a(2) =1a(3) =21a(4) =7a(5) =1a(6) =120a(7) =45a(8) =10a(9) =1a(10) =715a(11) =286a(12) =78a(13) =13a(14) =1a(15) =4368a(16) =1820a(17) =560a(18) =120a(19) =16a(20) =1a(21) =27132a(22) =11628a(23) =3876a(24) =969a(25) =171a(26) =19a(27) =1a(28) =170544a(29) =74613