a(n+1) = a(n) + n*a(n-1) - a(n-2) + a(n-3).

Terms

a(0) =1a(1) =1a(2) =1a(3) =2a(4) =5a(5) =13a(6) =37a(7) =112a(8) =363a(9) =1235a(10) =4427a(11) =16526a(12) =64351a(13) =259471a(14) =1083935a(15) =4668704a(16) =20732609a(17) =94607409a(18) =443476993a(19) =2130346450a(20) =10482534517a(21) =52740593933a(22) =271186949333