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%I #17 Jul 08 2021 06:23:46
%S 41,4441,44444444441,4444444444444444444444444441,
%T 4444444444444444444444444444444444444444444444444444441,
%U 4444444444444444444444444444444444444444444444444444444444444444444444444444444444444444444441
%N Primes of the form 40*R_k + 1, where R_k is the repunit (A002275) of length k.
%C Primes of the form (4*10^k - 31)/9. - _Vincenzo Librandi_, Nov 16 2010
%H Makoto Kamada, <a href="https://stdkmd.net/nrr/4/44441.htm#prime">Prime numbers of the form 44...441</a>.
%H <a href="/index/Pri#Pri_rep">Index entries for primes involving repunits</a>
%Y Cf. A056681 (corresponding k), A173768.
%K nonn
%O 1,1
%A _Rick L. Shepherd_, Mar 27 2004
%E Edited by _N. J. A. Sloane_, Feb 26 2010
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