Triangle T(n,k) (0 <= k <= n) with e.g.f. exp(x*y/(1-y)).

Terms

a(0) =1a(1) =0a(2) =0a(3) =0a(4) =1a(5) =0a(6) =0a(7) =0a(8) =2a(9) =0a(10) =0a(11) =0a(12) =2a(13) =6a(14) =0a(15) =0a(16) =0a(17) =0a(18) =12a(19) =24a(20) =0a(21) =0a(22) =0a(23) =0a(24) =6a(25) =72a(26) =120a(27) =0a(28) =0a(29) =0