a(n) = (6^n+12*(-7)^n)/13.

Terms

a(0) =1a(1) =-6a(2) =48a(3) =-300a(4) =2316a(5) =-14916a(6) =112188a(7) =-738660a(8) =5450556a(9) =-36474276a(10) =265397628a(11) =-1797317220a(12) =12944017596a(13) =-88431340836a(14) =632080079868