A216530 Numbers n such that 10^n+1 can be written in the form a^2+7*b^2.

1, 7, 19, 31, 49, 61, 67, 109, 133, 139, 157, 163, 211, 217

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