A216532 Prime numbers n such that 10^n+1 can be written in the form a^2+7*b^2.

7, 19, 31, 61, 67, 109, 139, 157, 163, 211

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