a(n) = (8*n + 1)^4.

Terms

a(0) =1a(1) =6561a(2) =83521a(3) =390625a(4) =1185921a(5) =2825761a(6) =5764801a(7) =10556001a(8) =17850625a(9) =28398241a(10) =43046721a(11) =62742241a(12) =88529281a(13) =121550625a(14) =163047361a(15) =214358881a(16) =276922881a(17) =352275361a(18) =442050625a(19) =547981281a(20) =671898241a(21) =815730721a(22) =981506241a(23) =1171350625a(24) =1387488001a(25) =1632240801a(26) =1908029761a(27) =2217373921