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%I #12 Nov 14 2019 18:24:03
%S 1,2,5,12,19,107,117,159,217,517,868,1412,1636,4051,5965,9128
%N Numbers n such that r(k) * 2^n + 1 is prime, where r() = A002275 the repunits and k is the number of decimal digits of 2^n.
%C a(1) through a(16) have been proved to be prime with WinPFGW. a(16) has 5495 digits. No more terms up to 11700.
%C Results were computed using the PrimeFormGW (PFGW) primality-testing program. - _Hugo Pfoertner_, Nov 14 2019
%e a(5)=19 because 111111 * 2^19 + 1 = 58254163969, a prime.
%K more,nonn,base
%O 1,2
%A _Jason Earls_, Jul 13 2004
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