a(n) = ((5 + sqrt(3))^n + (5 - sqrt(3))^n)/2.

Terms

a(0) =1a(1) =5a(2) =28a(3) =170a(4) =1084a(5) =7100a(6) =47152a(7) =315320a(8) =2115856a(9) =14221520a(10) =95666368a(11) =643790240a(12) =4333242304a(13) =29169037760a(14) =196359046912