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A216525
Numbers n such that (10^n-1)/9 can be written in the form a^2+7*b^2.
0
1, 2, 7, 13, 14, 19, 23, 37, 38, 47, 49, 53, 59, 71, 73, 83, 91, 98, 101, 103, 127, 133, 149, 151, 161, 191, 211, 259, 266, 317, 329
OFFSET
1,2
COMMENTS
These Repunit numbers of the form (10^n-1)/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.
CROSSREFS
Sequence in context: A145300 A240029 A340104 * A232637 A333383 A018322
KEYWORD
nonn
AUTHOR
V. Raman, Sep 08 2012
STATUS
approved