a(n) = (9*n + 7)^4.

Terms

a(0) =2401a(1) =65536a(2) =390625a(3) =1336336a(4) =3418801a(5) =7311616a(6) =13845841a(7) =24010000a(8) =38950081a(9) =59969536a(10) =88529281a(11) =126247696a(12) =174900625a(13) =236421376a(14) =312900721a(15) =406586896a(16) =519885601a(17) =655360000a(18) =815730721a(19) =1003875856