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A216530 Numbers n such that 10^n+1 can be written in the form a^2+7*b^2. 0
1, 7, 19, 31, 49, 61, 67, 109, 133, 139, 157, 163, 211, 217 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

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..14.

Samuel S. Wagstaff, Jr. The Cunningham Project

CROSSREFS

Sequence in context: A068229 A323594 A071696 * A114564 A191118 A298019

Adjacent sequences:  A216527 A216528 A216529 * A216531 A216532 A216533

KEYWORD

nonn

AUTHOR

V. Raman, Sep 08 2012

STATUS

approved

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Last modified November 13 02:59 EST 2019. Contains 329085 sequences. (Running on oeis4.)