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

Terms

a(0) =2a(1) =4a(2) =4a(3) =16a(4) =30a(5) =16a(6) =85a(7) =162a(8) =162a(9) =85a(10) =496a(11) =990a(12) =990a(13) =990a(14) =496a(15) =3004a(16) =6540a(17) =6370a(18) =6370a(19) =6540a(20) =3004a(21) =18565a(22) =43911a(23) =46818a(24) =37128a(25) =46818a(26) =43911a(27) =18565a(28) =116281a(29) =294140