%I #16 Jul 08 2021 06:20:57
%S 811,8111,811111111111111111111111111,
%T 811111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111,
%U 8111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111
%N Primes of the form 8*10^k + R_k, where R_k is the repunit (A002275) of length k.
%C The next term (a(6)) has 475 digits. - _Harvey P. Dale_, Sep 16 2016
%H Makoto Kamada, <a href="https://stdkmd.net/nrr/8/81111.htm#prime">Prime numbers of the form 811...11</a>.
%H <a href="/index/Pri#Pri_rep">Index entries for primes involving repunits</a>
%t Select[Table[FromDigits[PadRight[{8},n,1]],{n,150}],PrimeQ] (* _Harvey P. Dale_, Sep 16 2016 *)
%Y Cf. A002275, A056722 (corresponding k).
%K nonn
%O 1,1
%A _Rick L. Shepherd_, Apr 06 2004