a(n) is the least prime p such that exponent of highest power of 2 dividing 3p+1 equals n.

Terms

a(0) =3a(1) =17a(2) =13a(3) =5a(4) =53a(5) =149a(6) =1237a(7) =1109a(8) =853a(9) =2389a(10) =3413a(11) =17749a(12) =128341a(13) =70997a(14) =251221a(15) =415061a(16) =218453a(17) =2708821a(18) =27088213a(19) =29709653a(20) =3495253a(21) =85284181a(22) =13981013a(23) =39146837a(24) =794121557a(25) =1498764629a(26) =492131669a(27) =626349397a(28) =13779686741