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%I #17 Jan 04 2021 01:56:55
%S 0,1,3,17,19,33,39,169,453,611,883,1473,6511,9647,21593,39991,40157
%N Numbers k such that 8*10^k + 6*R_k + 3 is prime, where R_k = 11...1 is the repunit (A002275) of length k.
%C Also numbers k such that (26*10^k+7)/3 is prime.
%H Makoto Kamada, <a href="https://stdkmd.net/nrr/8/86669.htm#prime">Prime numbers of the form 866...669</a>.
%H <a href="/index/Pri#Pri_rep">Index entries for primes involving repunits</a>.
%F a(n) = A101075(n-1) + 1 for n >= 2.
%t Do[ If[ PrimeQ[(26*10^k + 7)/3], Print[k]], {k, 0, 10000}]
%Y Cf. A002275, A101075.
%K more,nonn
%O 1,3
%A _Robert G. Wilson v_, Jan 19 2005
%E a(15)-a(17) from Kamada data by _Robert Price_, Dec 14 2010
%E a(1)=0 inserted by _Georg Fischer_, Jan 03 2021
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