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

Terms

a(0) =5a(1) =13a(2) =47a(3) =175a(4) =653a(5) =2437a(6) =9095a(7) =33943a(8) =126677a(9) =472765a(10) =1764383a(11) =6584767a(12) =24574685a(13) =91713973a(14) =342281207a(15) =1277410855a(16) =4767362213a(17) =17792037997a(18) =66400789775a(19) =247811121103a(20) =924843694637