a(n) = Sum_{k=1..n} gcd(k,n)^(k-2).

Terms

a(0) =1a(1) =2a(2) =5a(3) =19a(4) =129a(5) =1306a(6) =16813a(7) =262181a(8) =4783059a(9) =100000214a(10) =2357947701a(11) =61917372083