a(n) = 2^n + 3^n.

Terms

a(0) =2a(1) =5a(2) =13a(3) =35a(4) =97a(5) =275a(6) =793a(7) =2315a(8) =6817a(9) =20195a(10) =60073a(11) =179195a(12) =535537a(13) =1602515a(14) =4799353a(15) =14381675a(16) =43112257a(17) =129271235a(18) =387682633a(19) =1162785755a(20) =3487832977a(21) =10462450355a(22) =31385253913a(23) =94151567435a(24) =282446313697a(25) =847322163875