a(n) = Sum_{d|n} d^(2*(d-2)).A308756a(n) = Sum_{d|n} d^(2*(d-2)).Terms a(0) =1a(1) =2a(2) =10a(3) =258a(4) =15626a(5) =1679627a(6) =282475250a(7) =68719476994External referencesoeis: A308756