a(n) = 7^n + 7*n + 1.

Terms

a(0) =2a(1) =15a(2) =64a(3) =365a(4) =2430a(5) =16843a(6) =117692a(7) =823593a(8) =5764858a(9) =40353671a(10) =282475320a(11) =1977326821a(12) =13841287286a(13) =96889010499a(14) =678223072948