a(1) = 2; a(n) is smallest prime > 3*a(n-1).

Terms

a(0) =2a(1) =7a(2) =23a(3) =71a(4) =223a(5) =673a(6) =2027a(7) =6089a(8) =18269a(9) =54829a(10) =164503a(11) =493523a(12) =1480571a(13) =4441721a(14) =13325171a(15) =39975553a(16) =119926691a(17) =359780077a(18) =1079340313a(19) =3238020943a(20) =9714062893a(21) =29142188683a(22) =87426566057a(23) =262279698173a(24) =786839094529