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

Terms

a(0) =1a(1) =1a(2) =1a(3) =1a(4) =2a(5) =3a(6) =1a(7) =4a(8) =10a(9) =20a(10) =1a(11) =7a(12) =28a(13) =84a(14) =210a(15) =1a(16) =11a(17) =66a(18) =286a(19) =1001a(20) =3003a(21) =1a(22) =16a(23) =136a(24) =816a(25) =3876a(26) =15504a(27) =54264a(28) =1a(29) =22