a(n) = (12*n + 3)^4.

Terms

a(0) =81a(1) =50625a(2) =531441a(3) =2313441a(4) =6765201a(5) =15752961a(6) =31640625a(7) =57289761a(8) =96059601a(9) =151807041a(10) =228886641a(11) =332150625a(12) =466948881a(13) =639128961a(14) =855036081a(15) =1121513121a(16) =1445900625a(17) =1836036801a(18) =2300257521