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A216531
Numbers n such that (10^n + 1)/11 is prime and can be written in the form a^2 + 7*b^2.
0
7, 19, 31, 67, 2137, 268207
OFFSET
1,1
COMMENTS
These exponents are congruent to {0, 1, 3} mod 6.
CROSSREFS
Cf. A001562.
Sequence in context: A234310 A141338 A237366 * A216564 A145042 A153892
KEYWORD
nonn
AUTHOR
V. Raman, Sep 08 2012
STATUS
approved