a(n) = the smallest prime number of the form k*2^n - 1, for k >= 1.

Terms

a(0) =2a(1) =3a(2) =3a(3) =7a(4) =31a(5) =31a(6) =127a(7) =127a(8) =1279a(9) =3583a(10) =5119a(11) =6143a(12) =8191a(13) =8191a(14) =81919a(15) =131071a(16) =131071a(17) =131071a(18) =524287a(19) =524287a(20) =14680063a(21) =14680063a(22) =109051903a(23) =109051903a(24) =654311423a(25) =738197503a(26) =738197503a(27) =2147483647a(28) =2147483647a(29) =2147483647