a(n) = Sum_{d|n} n^(d-1).

Terms

a(0) =1a(1) =3a(2) =10a(3) =69a(4) =626a(5) =7819a(6) =117650a(7) =2097673a(8) =43046803a(9) =1000010011a(10) =25937424602a(11) =743008621405