Irregular table of primitive prime factors of 8^n - 1.
7, 3, 73, 5, 13, 31, 151, 19, 127, 337, 17, 241, 262657, 11, 331, 23, 89, 599479, 37, 109, 79, 8191, 121369, 43, 5419, 631, 23311, 97, 257, 673, 103, 2143, 11119, 131071, 87211, 32377, 524287, 1212847, 41, 61, 1321, 92737, 649657, 67, 683, 20857, 47, 178481
1
T. D. Noe, Plot of irregular table up to n = 100
T. D. Noe, Table up to n = 100
(Mma) pp = {}; t = Table[f = Transpose[FactorInteger[8^n - 1]][[1]]; p = Complement[f, pp]; pp = Union[pp, p]; p, {n, 30}]; Flatten[t]
Cf. S000006 (number of primitive prime factors of 8^n - 1).
nonn,tabf
T. D. Noe, May 14 2014