Related to A045720 and A035101.

Terms

a(0) =0a(1) =0a(2) =1a(3) =18a(4) =285a(5) =4680a(6) =82845a(7) =1595790a(8) =33453945a(9) =760970700a(10) =18705542625a(11) =494764058250