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%I #10 Mar 07 2019 10:18:59
%S 2,5,8,24,35,116,208,231,237,303,1451,1512,2235,2612,4433,4499,5408,
%T 7331,11896,12821,23679,23900,59650,122082,151257,159656
%N Numbers k such that 5*10^k + 41 is prime.
%C For k>1, numbers such that the digit 5 followed by k-2 occurrences of the digit 0 followed by the digits 41 is prime (see Example section).
%C a(27) > 2*10^5.
%H Makoto Kamada, <a href="https://stdkmd.net/nrr">Factorization of near-repdigit-related numbers</a>.
%H Makoto Kamada, <a href="https://stdkmd.net/nrr/prime/primedifficulty.txt">Search for 50w41</a>
%e 2 is in this sequence because 5*10^2 + 41 = 541 is prime.
%e Initial terms and primes associated:
%e a(1) = 2, 541;
%e a(2) = 5, 500041;
%e a(3) = 8, 500000041;
%e a(4) = 24, 5000000000000000000000041;
%e a(5) = 35, 500000000000000000000000000000000041; etc.
%t Select[Range[0, 100000], PrimeQ[5*10^# + 41] &]
%o (PARI) isok(k) = ispseudoprime(5*10^k + 41); \\ _Altug Alkan_, Aug 27 2017
%Y Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269.
%K nonn,more,hard
%O 1,1
%A _Robert Price_, Aug 27 2017
%E a(24)-a(26) from _Robert Price_, Mar 07 2019
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