A216531 - OEIS

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A216531

Numbers n such that (10^n + 1)/11 is prime and can be written in the form a^2 + 7*b^2.

%I #18 May 02 2013 13:03:21

%S 7,19,31,67,2137,268207

%N Numbers n such that (10^n + 1)/11 is prime and can be written in the form a^2 + 7*b^2.

%C These exponents are congruent to {0, 1, 3} mod 6.

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

%Y Cf. A001562.

%K nonn

%O 1,1

%A _V. Raman_, Sep 08 2012