Triangle of partial products of binomials.

Terms

a(0) =1a(1) =1a(2) =1a(3) =1a(4) =2a(5) =2a(6) =1a(7) =3a(8) =9a(9) =9a(10) =1a(11) =4a(12) =24a(13) =96a(14) =96a(15) =1a(16) =5a(17) =50a(18) =500a(19) =2500a(20) =2500a(21) =1a(22) =6a(23) =90a(24) =1800a(25) =27000a(26) =162000a(27) =162000a(28) =1a(29) =7