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

Terms

a(0) =1a(1) =2a(2) =4a(3) =21a(4) =126a(5) =1394a(6) =16808a(7) =266305a(8) =4785157a(9) =100390882a(10) =2357947692a(11) =61978939050