a(n) = d(n-1) + d(n-2) + (n-1)[d(n-2) + 2d(n-3) + d(n-4)], where d(n), the derangement numbers, are given in A000166. (Let d(n) = 0 if n < 0.)

A109742

a(n) = d(n-1) + d(n-2) + (n-1)[d(n-2) + 2d(n-3) + d(n-4)], where d(n), the derangement numbers, are given in A000166. (Let d(n) = 0 if n < 0.)

Terms

    a(0) =1a(1) =2a(2) =5a(3) =9a(4) =27a(5) =123a(6) =693a(7) =4653a(8) =36111a(9) =317583a(10) =3118617a(11) =33804177a(12) =400755267a(13) =5156954019a(14) =71572594557

External references