a(n) is the least positive integer k such that 2^n-1 and k^n-1 are relatively prime.

Terms

a(0) =1a(1) =3a(2) =3a(3) =15a(4) =3a(5) =21a(6) =3a(7) =45a(8) =3a(9) =99a(10) =5a(11) =1365a(12) =3a(13) =3a(14) =3a(15) =765a(16) =3a(17) =399a(18) =3a(19) =1815a(20) =3a(21) =69a(22) =5a(23) =1365a(24) =3a(25) =3a(26) =3a(27) =435a(28) =3a(29) =35805