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%I #18 May 03 2024 18:55:27
%S 1,2,4,14,19,22,87,141,228,274,441,514,721,1674,1710,2725,2858,4658,
%T 19862,20175,25474,30309,34740
%N Numbers k such that 3*10^k + 97 is prime.
%C For k > 1, numbers k such that the digit 3 followed by k-2 occurrences of the digit 0 followed by the digits 97 is prime (see Example section).
%C a(24) > 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 30w97</a>.
%e 2 is in this sequence because 3*10^2 + 97 = 397 is prime.
%e Initial terms and associated primes:
%e a(1) = 1, 127;
%e a(2) = 2, 397;
%e a(3) = 4, 30097;
%e a(4) = 14, 300000000000097;
%e a(5) = 19, 30000000000000000097; etc.
%t Select[Range[0, 100000], PrimeQ[3*10^# + 97] &]
%o (PARI) isok(k) = isprime(3*10^k + 97); \\ _Michel Marcus_, Nov 22 2017
%Y Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269.
%K nonn,more,hard
%O 1,2
%A _Robert Price_, Nov 21 2017
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