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%I #21 Jul 08 2021 01:35:14
%S 2,3,6,11,30,128,183,375,2159,2568,3369,24989,38810,59558,74874
%N Numbers k such that 2*10^k + 4*R_k - 3 is prime, where R_k = 11...1 is the repunit (A002275) of length k.
%C Also numbers k such that (22*10^k - 31)/9 is prime.
%C a(16) > 10^5. - _Robert Price_, Apr 11 2015
%H Makoto Kamada, <a href="https://stdkmd.net/nrr/2/24441.htm#prime">Prime numbers of the form 244...441</a>.
%H <a href="/index/Pri#Pri_rep">Index entries for primes involving repunits</a>.
%F a(n) = A101957(n) + 1.
%t Do[ If[ PrimeQ[(22*10^n - 31)/9], Print[n]], {n, 0, 10000}]
%Y Cf. A002275, A101957.
%K more,nonn
%O 1,1
%A _Robert G. Wilson v_, Dec 17 2004
%E Addition of a(12) from Kamada data by _Robert Price_, Dec 13 2010
%E a(13) from Erik Branger May 01 2013 by _Ray Chandler_, Aug 16 2013
%E a(14)-a(15) from _Robert Price_, Apr 11 2015
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