a(n) = Bell(n) + n - 2 (cf. A000110).

Terms

a(0) =0a(1) =2a(2) =6a(3) =17a(4) =55a(5) =207a(6) =882a(7) =4146a(8) =21154a(9) =115983a(10) =678579a(11) =4213607a(12) =27644448a(13) =190899334a(14) =1382958558a(15) =10480142161a(16) =82864869819a(17) =682076806175