a(n) = 6*a(n-1) - a(n-2) - 4, a(0)=3, a(1)=7.

Terms

a(0) =3a(1) =7a(2) =35a(3) =199a(4) =1155a(5) =6727a(6) =39203a(7) =228487a(8) =1331715a(9) =7761799a(10) =45239075a(11) =263672647a(12) =1536796803a(13) =8957108167a(14) =52205852195a(15) =304278004999