a(n) = A000522(n) + 1.

Terms

a(0) =2a(1) =3a(2) =6a(3) =17a(4) =66a(5) =327a(6) =1958a(7) =13701a(8) =109602a(9) =986411a(10) =9864102a(11) =108505113a(12) =1302061346a(13) =16926797487a(14) =236975164806