Irregular table of primitive prime factors of 10^n + 1.
11, 101, 7, 13, 73, 137, 9091, 9901, 909091, 17, 5882353, 19, 52579, 3541, 27961, 23, 4093, 8779, 99990001, 859, 1058313049, 29, 281, 121499449, 211, 241, 2161, 353, 449, 641, 1409, 69857, 103, 4013, 21993833369, 999999000001, 909090909090909091, 1676321
1
T. D. Noe, Plot of irregular table up to n = 72
T. D. Noe, Table up to n = 72
Wikipedia, Cunningham project
The first 10 rows are
{11},
{101},
{7, 13},
{73, 137},
{9091},
{9901},
{909091},
{17, 5882353},
{19, 52579},
{3541, 27961}
(Mma) pp = {}; t = Table[f = Transpose[FactorInteger[10^n + 1]][[1]]; p = Complement[f, pp]; pp = Union[pp, p]; p, {n, 30}]; Flatten[t]
Cf. A112505 (number of primitive prime factors of 10^n + 1).
Cf. A003021 (largest factor of 10^n + 1).
nonn,tabf
T. D. Noe, May 14 2014