a(0) = 1, a(n+1) = (n+1)*(a(n) + n).

Terms

a(0) =1a(1) =1a(2) =4a(3) =18a(4) =84a(5) =440a(6) =2670a(7) =18732a(8) =149912a(9) =1349280a(10) =13492890a(11) =148421900a(12) =1781062932a(13) =23153818272a(14) =324153455990