a(n) is the smallest prime p such that p + 1 has 2n divisors.

Terms

a(0) =2a(1) =5a(2) =11a(3) =23a(4) =47a(5) =59a(6) =191a(7) =167a(8) =179a(9) =239a(10) =5119a(11) =359a(12) =20479a(13) =2111a(14) =719a(15) =839a(16) =1114111a(17) =1259a(18) =786431a(19) =3023a(20) =2879a(21) =15359a(22) =348127231a(23) =3359a(24) =22031a(25) =266239a(26) =6299a(27) =6719a(28) =22280142847a(29) =5039