a(n) = Bell(n+1)-Bell(n)-1, n>0.

Terms

a(0) =0a(1) =0a(2) =2a(3) =9a(4) =36a(5) =150a(6) =673a(7) =3262a(8) =17006a(9) =94827a(10) =562594a(11) =3535026a(12) =23430839a(13) =163254884a(14) =1192059222a(15) =9097183601a(16) =72384727656a(17) =599211936354