Irregular table of primitive prime factors of 8^n + 1.
3, 5, 13, 19, 17, 241, 11, 331, 37, 109, 43, 5419, 97, 257, 673, 87211, 41, 61, 1321, 67, 683, 20857, 433, 38737, 2731, 22366891, 29, 113, 1429, 14449, 18837001, 193, 65537, 22253377, 307, 2857, 6529, 43691, 246241, 279073, 571, 174763, 160465489, 61681
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. A158895 (primitive prime factors of 2^n + 1), S000013 (number of primitive prime factors of 8^n + 1).
nonn,tabf
T. D. Noe, May 14 2014