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%I #33 Apr 20 2024 16:19:07
%S 0,1,2,4,5,12,60,109,181,245,412,887,2477,2918,4622,6240,6253,7684,
%T 14630,20932,49801,254107,275671,380056
%N Numbers k such that 10^k + 3*R_k + 4 is prime, where R_k = 11...1 is the repunit (A002275) of length k.
%C Also numbers k such that (4*10^k + 11)/3 is prime.
%C a(22) > 2*10^5. - _Robert Price_, Feb 17 2018
%H Makoto Kamada, <a href="https://stdkmd.net/nrr/1/13337.htm#prime">Prime numbers of the form 133...337</a>.
%H <a href="/index/Pri#Pri_rep">Index entries for primes involving repunits</a>.
%F a(n) = A102013(n-1) + 1.
%t Do[ If[ PrimeQ[(4*10^n + 11)/3], Print[n]], {n, 0, 10000}]
%Y Cf. A002275, A102013.
%K more,nonn,changed
%O 1,3
%A _Robert G. Wilson v_, Dec 16 2004
%E Addition of a(19)-a(20) from Kamada data by _Robert Price_, Dec 10 2010
%E 0 added by _Arkadiusz Wesolowski_, Mar 10 2011
%E a(21) from Erik Branger May 01 2013 by _Ray Chandler_, Aug 16 2013
%E a(22)-a(24) from _Tyler Busby_, Apr 20 2024
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