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%I #13 Jul 08 2021 06:24:29
%S 911,911111,911111111111111111111,
%T 911111111111111111111111111111111111111111,
%U 911111111111111111111111111111111111111111111111,911111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111
%N Primes of the form 9*10^k + R_k, where R_k is the repunit (A002275) of length k.
%H Makoto Kamada, <a href="https://stdkmd.net/nrr/9/91111.htm#prime">Prime numbers of the form 911...11</a>.
%H H. C. Williams, <a href="http://www.jstor.org/stable/2006356">Some primes with interesting digit patterns</a>, Math. Comp. vol 32 no 144 (1978) pp 1306-1310, Table 2, r=9.
%H <a href="/index/Pri#Pri_rep">Index entries for primes involving repunits</a>
%t Select[Table[FromDigits[PadRight[{9},n,1]],{n,60}],PrimeQ] (* _Harvey P. Dale_, Jun 18 2017 *)
%Y Cf. A002275, A056726 (corresponding k).
%K nonn
%O 1,1
%A _Rick L. Shepherd_, Apr 06 2004
%E One more term from _Harvey P. Dale_, Jun 18 2017
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