a(n) = 12^n - n^4.

Terms

a(0) =1a(1) =11a(2) =128a(3) =1647a(4) =20480a(5) =248207a(6) =2984688a(7) =35829407a(8) =429977600a(9) =5159773791a(10) =61917354224a(11) =743008356047