a(n) = nextprime(3^n) - nextprime(2^n).

Terms

a(0) =0a(1) =2a(2) =6a(3) =18a(4) =66a(5) =214a(6) =666a(7) =2072a(8) =6306a(9) =19166a(10) =58020a(11) =175114a(12) =527358a(13) =1586122a(14) =4766560a(15) =14316138a(16) =42981210a(17) =129009096a(18) =387158352a(19) =1161737214a(20) =3485735826a(21) =10458256090a(22) =31376865294a(23) =94134790242a(24) =282412759224a(25) =847255054990