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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

%I

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

%N Prime 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 1,1

%A _V. Raman_, Sep 08 2012

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Last modified June 20 12:49 EDT 2021. Contains 345164 sequences. (Running on oeis4.)