A093943 - OEIS

%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