a(n) = 6*a(n-1) - a(n-2) + 2, with a(0)=1, a(1)=4.

Terms

a(0) =1a(1) =4a(2) =25a(3) =148a(4) =865a(5) =5044a(6) =29401a(7) =171364a(8) =998785a(9) =5821348a(10) =33929305a(11) =197754484a(12) =1152597601a(13) =6717831124a(14) =39154389145a(15) =228208503748