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A216530
Numbers n such that 10^n+1 can be written in the form a^2+7*b^2.
0
1, 7, 19, 31, 49, 61, 67, 109, 133, 139, 157, 163, 211, 217
OFFSET
1,2
COMMENTS
These numbers of the form 10^n+1 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: A068229 A323594 A071696 * A114564 A191118 A298019
KEYWORD
nonn
AUTHOR
V. Raman, Sep 08 2012
STATUS
approved