a(n) = 3^(2*n + 3) + 2^n.

Terms

a(0) =28a(1) =245a(2) =2191a(3) =19691a(4) =177163a(5) =1594355a(6) =14348971a(7) =129140291a(8) =1162261723a(9) =10460353715a(10) =94143179851a(11) =847288611491