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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

Cf. 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 October 16 08:15 EDT 2019. Contains 328051 sequences. (Running on oeis4.)