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

Terms

a(0) =256a(1) =20736a(2) =160000a(3) =614656a(4) =1679616a(5) =3748096a(6) =7311616a(7) =12960000a(8) =21381376a(9) =33362176a(10) =49787136a(11) =71639296a(12) =100000000a(13) =136048896a(14) =181063936a(15) =236421376a(16) =303595776a(17) =384160000a(18) =479785216a(19) =592240896a(20) =723394816a(21) =875213056a(22) =1049760000a(23) =1249198336a(24) =1475789056a(25) =1731891456