A216515 - OEIS

%I #5 Sep 08 2012 16:07:26

%S 3,7,13,19,31,61,67,97,103,109,127,199,229,241,271,349,457,499,523,

%T 601,607,673,733,751,823,877,907,997

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

%C These Mersenne numbers have no prime factors congruent to 3, 5 or 6 (mod 7) raised 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