a(n) = 4^n + n^4.

Terms

a(0) =1a(1) =5a(2) =32a(3) =145a(4) =512a(5) =1649a(6) =5392a(7) =18785a(8) =69632a(9) =268705a(10) =1058576a(11) =4208945a(12) =16797952a(13) =67137425a(14) =268473872a(15) =1073792449a(16) =4295032832a(17) =17179952705a(18) =68719581712a(19) =274878037265