a(n) = 11^n + 7^n - 1.

Terms

a(0) =1a(1) =17a(2) =169a(3) =1673a(4) =17041a(5) =177857a(6) =1889209a(7) =20310713a(8) =220123681a(9) =2398301297a(10) =26219899849a(11) =287288997353