Triangle of numbers where k-th row contains (ij)!/(i!j!) with i+j = k+1, 1 <= i <= k.

Terms

a(0) =1a(1) =1a(2) =1a(3) =1a(4) =6a(5) =1a(6) =1a(7) =60a(8) =60a(9) =1a(10) =1a(11) =840a(12) =10080a(13) =840a(14) =1a(15) =1a(16) =15120a(17) =3326400a(18) =3326400a(19) =15120a(20) =1a(21) =1a(22) =332640a(23) =1816214400a(24) =36324288000a(25) =1816214400a(26) =332640a(27) =1a(28) =1a(29) =8648640