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

Terms

a(0) =1a(1) =1a(2) =1a(3) =1a(4) =1a(5) =4a(6) =1a(7) =10a(8) =3a(9) =1a(10) =20a(11) =21a(12) =1a(13) =35a(14) =84a(15) =12a(16) =1a(17) =56a(18) =252a(19) =120a(20) =1a(21) =84a(22) =630a(23) =660a(24) =55a(25) =1a(26) =120a(27) =1386a(28) =2640a(29) =715