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%I #26 Feb 01 2023 23:07:08
%S 1,2,4,14,25,32,56,62,811,812,1084,2533,11924,49552
%N Numbers k such that 10^k + 2*R_k + 5 is prime, where R_k = 11...1 is the repunit (A002275) of length k.
%C Also numbers k such that (11*10^k + 43)/9 is prime.
%C a(15) > 10^5. - _Robert Price_, Jan 16 2015
%C a(15) > 2*10^5. - _Tyler Busby_, Feb 01 2023
%H Makoto Kamada, <a href="https://stdkmd.net/nrr/1/12227.htm#prime">Prime numbers of the form 122...227</a>.
%H <a href="/index/Pri#Pri_rep">Index entries for primes involving repunits</a>.
%F a(n) = A102010(n) + 1.
%t Do[ If[ PrimeQ[(11*10^n + 43)/9], Print[n]], {n, 0, 10000}]
%Y Cf. A002275, A102010.
%K more,nonn
%O 1,2
%A _Robert G. Wilson v_, Dec 16 2004
%E Addition of a(13) from Kamada data by _Robert Price_, Dec 12 2010
%E a(14) from Erik Branger May 01 2013 by _Ray Chandler_, Aug 16 2013
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