a(n) = 7^n + 6.

Terms

a(0) =7a(1) =13a(2) =55a(3) =349a(4) =2407a(5) =16813a(6) =117655a(7) =823549a(8) =5764807a(9) =40353613a(10) =282475255a(11) =1977326749a(12) =13841287207a(13) =96889010413a(14) =678223072855