Smallest prime with at least n 1's when written in binary.

Terms

a(0) =2a(1) =3a(2) =7a(3) =23a(4) =31a(5) =127a(6) =127a(7) =383a(8) =991a(9) =2039a(10) =3583a(11) =6143a(12) =8191a(13) =63487a(14) =63487a(15) =129023a(16) =131071a(17) =522239a(18) =524287a(19) =1966079a(20) =4128767a(21) =14680063a(22) =14680063a(23) =33546239a(24) =67108351a(25) =201064447a(26) =260046847a(27) =536739839a(28) =1073479679a(29) =2147483647