a(n) = (1 - (-12)^n)/13.

Terms

a(0) =1a(1) =-11a(2) =133a(3) =-1595a(4) =19141a(5) =-229691a(6) =2756293a(7) =-33075515a(8) =396906181a(9) =-4762874171a(10) =57154490053a(11) =-685853880635