a(n) = 6*a(n-1) - a(n-2) - 2 with a(0) = 1, a(1) = 3.

Terms

a(0) =1a(1) =3a(2) =15a(3) =85a(4) =493a(5) =2871a(6) =16731a(7) =97513a(8) =568345a(9) =3312555a(10) =19306983a(11) =112529341a(12) =655869061a(13) =3822685023a(14) =22280241075a(15) =129858761425a(16) =756872327473