Irregular table of primitive prime factors of 9^n + 1.
2, 5, 41, 73, 17, 193, 1181, 6481, 29, 16493, 21523361, 530713, 42521761, 5501, 570461, 97, 577, 769, 53, 4795973261, 430697, 647753, 47763361, 926510094425921, 956353, 1743831169, 282429005041, 5301533, 25480398173, 14401, 128653413121, 2857, 109688713, 89
1
T. D. Noe, Plot of irregular table up to n = 96
T. D. Noe, Table up to n = 96
(Mma) pp = {}; t = Table[f = Transpose[FactorInteger[9^n + 1]][[1]]; p = Complement[f, pp]; pp = Union[pp, p]; p, {n, 30}]; Flatten[t]
Cf. S000014 (number of primitive prime factors of 9^n + 1), S000045 (primitive prime factors of 3^n + 1).
Cf. A002592 (largest prime factor of 9^n + 1).
nonn,tabf
T. D. Noe, May 14 2014