a(n) = ((6+sqrt(5))^n+(6-sqrt(5))^n)/2.

Terms

a(0) =1a(1) =6a(2) =41a(3) =306a(4) =2401a(5) =19326a(6) =157481a(7) =1290666a(8) =10606081a(9) =87262326a(10) =718359401a(11) =5915180706a(12) =48713027041a(13) =401185722606