a(n) = (5*n + 4)^4.

Terms

a(0) =256a(1) =6561a(2) =38416a(3) =130321a(4) =331776a(5) =707281a(6) =1336336a(7) =2313441a(8) =3748096a(9) =5764801a(10) =8503056a(11) =12117361a(12) =16777216a(13) =22667121a(14) =29986576a(15) =38950081a(16) =49787136a(17) =62742241a(18) =78074896a(19) =96059601a(20) =116985856a(21) =141158161