a(n) = n*a(n-1) - a(n-2), with a(-1) = 0, a(0) = 1.

Terms

a(0) =0a(1) =1a(2) =1a(3) =1a(4) =2a(5) =7a(6) =33a(7) =191a(8) =1304a(9) =10241a(10) =90865a(11) =898409a(12) =9791634a(13) =116601199a(14) =1506023953a(15) =20967734143a(16) =313009988192