Triangle read by rows: T(n,k) = binomial(n+1,k+1) * binomial(3*n-2*k+1,k) / (n+1), 0<=k<=n.

Terms

a(0) =1a(1) =1a(2) =1a(3) =1a(4) =5a(5) =1a(6) =1a(7) =12a(8) =15a(9) =1a(10) =1a(11) =22a(12) =72a(13) =35a(14) =1a(15) =1a(16) =35a(17) =220a(18) =300a(19) =70a(20) =1a(21) =1a(22) =51a(23) =525a(24) =1430a(25) =990a(26) =126a(27) =1a(28) =1a(29) =70