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A216532 Prime numbers n such that 10^n+1 can be written in the form a^2+7*b^2. 0
7, 19, 31, 61, 67, 109, 139, 157, 163, 211 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

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.

LINKS

Table of n, a(n) for n=1..10.

Samuel S. Wagstaff, Jr. The Cunningham Project

CROSSREFS

Sequence in context: A191118 A298019 A169605 * A249375 A212492 A234310

Adjacent sequences:  A216529 A216530 A216531 * A216533 A216534 A216535

KEYWORD

nonn

AUTHOR

V. Raman, Sep 08 2012

STATUS

approved

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Last modified November 22 16:22 EST 2019. Contains 329396 sequences. (Running on oeis4.)