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A216549
Numbers n such that (10^n-1)/9 is prime, but cannot be written in the form a^2 + 3*b^2.
0
2, 23, 317, 1031, 86453
OFFSET
1,1
COMMENTS
The exponent is congruent to 2 mod 3.
LINKS
CROSSREFS
Subsequence of A004023.
Sequence in context: A088641 A077203 A173935 * A091693 A276025 A211925
KEYWORD
nonn
AUTHOR
V. Raman, Sep 08 2012
STATUS
approved