a(n) = 4^n - prevprime(4^n).

Terms

a(0) =1a(1) =3a(2) =3a(3) =5a(4) =3a(5) =3a(6) =3a(7) =15a(8) =5a(9) =3a(10) =3a(11) =3a(12) =5a(13) =57a(14) =35a(15) =5a(16) =41a(17) =5a(18) =45a(19) =87a(20) =11a(21) =17a(22) =21a(23) =59a(24) =27a(25) =47a(26) =33a(27) =5a(28) =27a(29) =93