Next prime after 3^n.

Terms

a(0) =2a(1) =5a(2) =11a(3) =29a(4) =83a(5) =251a(6) =733a(7) =2203a(8) =6563a(9) =19687a(10) =59051a(11) =177167a(12) =531457a(13) =1594331a(14) =4782971a(15) =14348909a(16) =43046747a(17) =129140197a(18) =387420499a(19) =1162261523a(20) =3486784409a(21) =10460353259a(22) =31381059613a(23) =94143178859a(24) =282429536483a(25) =847288609457