a(n) = (9*n+3)^4.

Terms

a(0) =81a(1) =20736a(2) =194481a(3) =810000a(4) =2313441a(5) =5308416a(6) =10556001a(7) =18974736a(8) =31640625a(9) =49787136a(10) =74805201a(11) =108243216a(12) =151807041a(13) =207360000a(14) =276922881a(15) =362673936a(16) =466948881a(17) =592240896a(18) =741200625a(19) =916636176