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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 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
COMMENTS
The exponent is congruent to 2 mod 3.
LINKS
Table of n, a(n) for n=1..5.
Samuel S. Wagstaff, Jr., The Cunningham Project
CROSSREFS
Subsequence of A004023.
Sequence in context: A088641 A077203 A173935 * A091693 A276025 A211925
Adjacent sequences: A216546 A216547 A216548 * A216550 A216551 A216552
KEYWORD
nonn
AUTHOR
V. Raman, Sep 08 2012
STATUS
approved

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Last modified August 30 09:19 EDT 2024. Contains 375532 sequences. (Running on oeis4.)