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

Terms

a(0) =0a(1) =2401a(2) =38416a(3) =194481a(4) =614656a(5) =1500625a(6) =3111696a(7) =5764801a(8) =9834496a(9) =15752961a(10) =24010000a(11) =35153041a(12) =49787136a(13) =68574961a(14) =92236816a(15) =121550625a(16) =157351936a(17) =200533921a(18) =252047376a(19) =312900721a(20) =384160000a(21) =466948881a(22) =562448656a(23) =671898241a(24) =796594176a(25) =937890625a(26) =1097199376