a(n) = (6*n + 3)^4.

Terms

a(0) =81a(1) =6561a(2) =50625a(3) =194481a(4) =531441a(5) =1185921a(6) =2313441a(7) =4100625a(8) =6765201a(9) =10556001a(10) =15752961a(11) =22667121a(12) =31640625a(13) =43046721a(14) =57289761a(15) =74805201a(16) =96059601a(17) =121550625a(18) =151807041a(19) =187388721a(20) =228886641a(21) =276922881a(22) =332150625a(23) =395254161a(24) =466948881a(25) =547981281a(26) =639128961