Column 1 of triangle in A250104 (or A124323).

Terms

a(0) =0a(1) =0a(2) =3a(3) =4a(4) =20a(5) =66a(6) =287a(7) =1296a(8) =6435a(9) =34250a(10) =194942a(11) =1179036a(12) =7544121a(13) =50865920a(14) =360167355a(15) =2670210640a(16) =20673196460a(17) =166753291806