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

Terms

a(0) =0a(1) =6561a(2) =104976a(3) =531441a(4) =1679616a(5) =4100625a(6) =8503056a(7) =15752961a(8) =26873856a(9) =43046721a(10) =65610000a(11) =96059601a(12) =136048896a(13) =187388721a(14) =252047376a(15) =332150625a(16) =429981696a(17) =547981281a(18) =688747536a(19) =855036081a(20) =1049760000a(21) =1275989841a(22) =1536953616a(23) =1836036801a(24) =2176782336a(25) =2562890625