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%I #12 Jul 08 2021 05:31:05
%S 877,8777777777,8777777777777777,877777777777777777777777777777777,
%T 877777777777777777777777777777777777777,
%U 877777777777777777777777777777777777777777777777777777777777777777
%N Primes of the form 8*10^k + 7*R_k, where R_k is the repunit (A002275) of length k.
%H Makoto Kamada, <a href="https://stdkmd.net/nrr/8/87777.htm#prime">Prime numbers of the form 877...77</a>.
%H <a href="/index/Pri#Pri_rep">Index entries for primes involving repunits</a>
%Y Cf. A002275, A056724 (corresponding k).
%K nonn
%O 1,1
%A _Rick L. Shepherd_, Apr 17 2004