Triangle read by rows: binomial(3*n,3*k), 0 <= k <= n.

Terms

a(0) =1a(1) =1a(2) =1a(3) =1a(4) =20a(5) =1a(6) =1a(7) =84a(8) =84a(9) =1a(10) =1a(11) =220a(12) =924a(13) =220a(14) =1a(15) =1a(16) =455a(17) =5005a(18) =5005a(19) =455a(20) =1a(21) =1a(22) =816a(23) =18564a(24) =48620a(25) =18564a(26) =816a(27) =1a(28) =1a(29) =1330