%I
%S 0,2,6,15,18,26,51,75,86,114,257,275,537,753,914,1944,18431,18741,
%T 21281,28272,31002,71621,84170,110961
%N Numbers k such that (74*10^k + 313)/9 is prime.
%C For k > 1, numbers such that the digit 8 followed by k2 occurrences of the digit 2 followed by the digits 57 is prime (see Example section).
%C a(25) > 2*10^5.
%H Makoto Kamada, <a href="https://stdkmd.net/nrr">Factorization of nearrepdigitrelated numbers</a>.
%H Makoto Kamada, <a href="https://stdkmd.net/nrr/prime/primedifficulty.txt">Search for 82w57</a>.
%e 2 is in this sequence because (74*10^2 + 313)/9 = 857 is prime.
%e Initial terms and primes associated:
%e a(1) = 0, 43;
%e a(2) = 2, 857;
%e a(3) = 6, 8222257;
%e a(4) = 15, 8222222222222257;
%e a(5) = 18, 8222222222222222257; etc.
%t Select[Range[0, 100000], PrimeQ[(74*10^# + 313)/9] &]
%o (PARI) isok(k) = isprime((74*10^k + 313)/9); \\ _Michel Marcus_, Nov 12 2017
%Y Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269.
%K nonn,more,hard
%O 1,2
%A _Robert Price_, Nov 11 2017
%E a(24) from _Robert Price_, Jun 14 2019
