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%I #14 May 25 2024 19:34:49
%S 3,6,10,16,22,30,33,48,61,66,147,300,372,925,1750,2026,2721,3916,5704,
%T 6856,12883,57333,92244,147649,150763
%N Numbers k such that (23*10^k - 59)/9 is prime.
%C For k > 1, numbers k such that the digit 2 followed by k-2 occurrences of the digit 5 followed by the digits 49 is prime (see Example section).
%C a(26) > 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/prime_difficulty.txt">Search for 25w49</a>.
%e 6 is in this sequence because (23*10^6 - 59)/9 = is prime.
%e Initial terms and associated primes:
%e a(1) = 3, 2549;
%e a(2) = 6, 2555549;
%e a(3) = 10, 25555555549;
%e a(4) = 16, 25555555555555549;
%e a(5) = 22, 25555555555555555555549; etc.
%t Select[Range[0, 100000], PrimeQ[(23*10^# - 59)/9] &]
%o (PARI) isok(n) = isprime((23*10^n - 59)/9); \\ _Indranil Ghosh_, Mar 09 2017
%Y Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269.
%K nonn,more,hard
%O 1,1
%A _Robert Price_, Mar 09 2017
%E a(24)-a(25) from _Robert Price_, May 29 2018
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