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%I #7 Sep 23 2019 13:32:52
%S 1,1,1,1,1,4,1,27,14,34,6,132,97,1,500,1816,1292,136,2445,15,1934,
%T 5472,1584,2734,21022,5870
%N Least k such that k*(2^p-1)*(k*(2^p-1)-1)-1 is prime, where 2^p-1 runs through the Mersenne primes.
%e 1*(2^2-1)*(1*(2^2-1)-1)-1=5 prime, 2^2-1 first Mersenne prime, a(1)=1;
%e 1*(2^3-1)*(1*(2^3-1)-1)-1=41 prime, 2^3-1 second Mersenne prime, a(2)=1.
%Y Cf. A137907, A137908, A137909.
%K nonn,hard,more
%O 1,6
%A _Pierre CAMI_, Feb 22 2008
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