

A216526


Prime numbers n such that (10^n1)/9 can be written in the form a^2+7*b^2.


0



2, 7, 13, 19, 23, 37, 47, 53, 59, 71, 73, 83, 101, 103, 127, 149, 151, 191, 211, 317
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OFFSET

1,1


COMMENTS

These repunit numbers of the form (10^n1)/9 have no prime factors congruent to 3 (mod 7) or 5 (mod 7) or 6 (mod 7) to an odd power. Also the power of 2 is not 1.


LINKS



MATHEMATICA

Select[Prime[Range[70]], Length[Solve[a^2+7b^2==(10^#1)/9, {a, b}, Integers]] > 0&] (* Harvey P. Dale, Aug 19 2015 *)


CROSSREFS



KEYWORD

nonn


AUTHOR



STATUS

approved



