A216530 - OEIS

%I #6 Sep 08 2012 15:25:59

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

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

%C 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.

%H Samuel S. Wagstaff, Jr. <a href="http://homes.cerias.purdue.edu/~ssw/cun/index.html">The Cunningham Project</a>

%K nonn

%O 1,2

%A _V. Raman_, Sep 08 2012