If 2*n = Sum (2^e_k) then a(n) = Sum (e_k^n).

Terms

a(0) =1a(1) =4a(2) =9a(3) =81a(4) =244a(5) =793a(6) =2316a(7) =65536a(8) =262145a(9) =1049600a(10) =4196353a(11) =17308657a(12) =68703188a(13) =273234809a(14) =1088123500a(15) =152587890625a(16) =762939453126