a(n) = 12^n-n^2.

Terms

a(0) =1a(1) =11a(2) =140a(3) =1719a(4) =20720a(5) =248807a(6) =2985948a(7) =35831759a(8) =429981632a(9) =5159780271a(10) =61917364124a(11) =743008370567