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%I #26 Jul 04 2021 19:04:45
%S 0,1,2,5,8,11,29,31,182,296,491,41315
%N Numbers k such that 40*R_k + 3 is prime, where R_k = 11...1 is the repunit (A002275) of length k.
%C Also numbers k such that (4*10^(k+1)-13)/9 is prime.
%C a(13) > 10^5. - _Robert Price_, Nov 01 2014
%H Makoto Kamada, <a href="https://stdkmd.net/nrr/4/44443.htm#prime">Prime numbers of the form 44...443</a>.
%H <a href="/index/Pri#Pri_rep">Index entries for primes involving repunits</a>
%F a(n) = A096845(n) - 1. - _Robert Price_, Nov 01 2014
%t Do[ If[ PrimeQ[ 40*(10^n - 1)/9 + 3], Print[n]], {n, 0, 5000}]
%Y Cf. A002275, A096845.
%K hard,more,nonn
%O 1,3
%A _Robert G. Wilson v_, Aug 09 2000
%E a(12) derived from A096845 by _Robert Price_, Nov 01 2014
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