a(n) = Bell(n) - 2^n + n.

Terms

a(0) =0a(1) =0a(2) =0a(3) =0a(4) =3a(5) =25a(6) =145a(7) =756a(8) =3892a(9) =20644a(10) =114961a(11) =676533a(12) =4209513a(13) =27636258a(14) =190882952a(15) =1382925792a(16) =10480076627a(17) =82864738749a(18) =682076544033