Triangle T(n,k) read by rows; related to number of preorders.

Terms

a(0) =1a(1) =0a(2) =2a(3) =0a(4) =3a(5) =6a(6) =0a(7) =0a(8) =20a(9) =24a(10) =0a(11) =0a(12) =15a(13) =130a(14) =120a(15) =0a(16) =0a(17) =0a(18) =210a(19) =924a(20) =720a(21) =0a(22) =0a(23) =0a(24) =105a(25) =2380a(26) =7308a(27) =5040a(28) =0a(29) =0