a(n) = Sum_{d|n} d^(d-2).

Terms

a(0) =1a(1) =2a(2) =4a(3) =18a(4) =126a(5) =1301a(6) =16808a(7) =262162a(8) =4782973a(9) =100000127a(10) =2357947692a(11) =61917365541