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%I #25 Jul 08 2021 06:25:19
%S 59,55555559,555555555559,555555555555555559,
%T 55555555555555555555555559,55555555555555555555555555555559
%N Primes of the form 50*R_k + 9, where R_k is the repunit (A002275) of length k.
%C Primes of the form (5*10^k + 31)/9. - _Vincenzo Librandi_, Nov 17 2010
%H Makoto Kamada, <a href="https://stdkmd.net/nrr/5/55559.htm#prime">Prime numbers of the form 55...559</a>.
%H <a href="/index/Pri#Pri_rep">Index entries for primes involving repunits</a>
%F a(n) = (50*10^A056687(n) + 31)/9 = (5*10^A099418(n) + 31)/9.
%Y Cf. A056687 (corresponding k), A099418.
%K nonn
%O 1,1
%A _Rick L. Shepherd_, Mar 28 2004
%E Edited by _Ray Chandler_, Feb 27 2012
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