The OEIS is supported by the many generous donors to the OEIS Foundation.
%I #17 May 27 2024 02:07:16
%S 1,2,3,7,9,15,18,23,39,147,1104,1158,1466,1514,1935,2149,2203,2553,
%T 2730,7169,9807,17684,23828,25824,27207,55679,94964,122977,206927
%N Numbers k such that 3*10^k + 37 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 37 is prime (see Example section).
%C a(30) > 3*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 30w37</a>.
%e 2 is in this sequence because 3*10^2 + 37 = 337 is prime.
%e Initial terms and associated primes:
%e a(1) = 1, 67;
%e a(2) = 2, 337;
%e a(3) = 3, 3037;
%e a(4) = 7, 30000037;
%e a(5) = 9, 3000000037; etc.
%t Select[Range[0, 100000], PrimeQ[3*10^# + 37] &]
%Y Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269.
%K nonn,more,hard
%O 1,2
%A _Robert Price_, Oct 23 2017
%E a(28) from _Robert Price_, Aug 15 2018
%E a(29) from _Robert Price_, Oct 26 2023