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

Terms

a(0) =1a(1) =1a(2) =-1a(3) =-3a(4) =-3a(5) =3a(6) =27a(7) =117a(8) =513a(9) =2655a(10) =16623a(11) =123057a(12) =1047717a(13) =10048203a(14) =106958115a(15) =1249780653a(16) =15892557417a(17) =218391870807