a(n) = 3^n + 4.

Terms

a(0) =5a(1) =7a(2) =13a(3) =31a(4) =85a(5) =247a(6) =733a(7) =2191a(8) =6565a(9) =19687a(10) =59053a(11) =177151a(12) =531445a(13) =1594327a(14) =4782973a(15) =14348911a(16) =43046725a(17) =129140167a(18) =387420493a(19) =1162261471a(20) =3486784405a(21) =10460353207a(22) =31381059613a(23) =94143178831a(24) =282429536485a(25) =847288609447