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

Terms

a(0) =1a(1) =1a(2) =1a(3) =3a(4) =6a(5) =3a(6) =6a(7) =30a(8) =60a(9) =60a(10) =10a(11) =90a(12) =360a(13) =840a(14) =1260a(15) =15a(16) =210a(17) =1365a(18) =5460a(19) =15015a(20) =30030a(21) =21a(22) =420a(23) =3990a(24) =23940a(25) =101745a(26) =325584a(27) =813960a(28) =28a(29) =756