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%I #12 Jan 17 2019 13:44:10
%S 2,3,5,6,9,14,17,20,54,56,165,902,1023,6483,14174,18411,20025,27411,
%T 49583,59589,66896,97329
%N Numbers k such that (38*10^k + 187)/9 is prime.
%C For k > 1, numbers such that the digit 4 followed by k-2 occurrences of the digit 2 followed by the digits 43 is prime (see Example section).
%C a(23) > 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 42w43</a>
%e 2 is in this sequence because (38*10^2 + 187)/9 = 443 is prime.
%e Initial terms and primes associated:
%e a(1) = 2, 443;
%e a(2) = 3, 4243;
%e a(3) = 5, 422243;
%e a(4) = 6, 4222243;
%e a(5) = 9, 4222222243; etc.
%t Select[Range[0, 100000], PrimeQ[38*10^# + 187)/9] &]
%t Select[Range[2,100000],PrimeQ[100*FromDigits[PadRight[{4},#-1,2]]+43]&] (* _Harvey P. Dale_, Jan 16 2018 *)
%o (PARI) is(k) = ispseudoprime((38*10^k + 187)/9) \\ _Iain Fox_, Nov 24 2017
%Y Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269.
%K nonn,more,hard
%O 1,1
%A _Robert Price_, Nov 24 2017
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