# Greetings from The On-Line Encyclopedia of Integer Sequences! http://oeis.org/

Search: id:a286395
Showing 1-1 of 1

%I A286395 #21 May 25 2024 14:28:24
%S A286395 1,3,7,8,9,11,15,19,29,55,76,159,266,311,394,908,1732,1875,4335,6334,
%T A286395 7641,16421,33721,139239,157705,160143
%N A286395 Numbers k such that (17*10^k + 67)/3 is prime.
%C A286395 For k > 1, numbers k such that the digit 5 followed by k-2 occurrences of the digit 6 followed by the digits 89 is prime (see Example section).
%C A286395 a(27) > 2*10^5.
%H A286395 Makoto Kamada, <a href="https://stdkmd.net/nrr">Factorization of near-repdigit-related numbers</a>.
%H A286395 Makoto Kamada, <a href="https://stdkmd.net/nrr/prime/prime_difficulty.txt">Search for 56w89</a>.
%e A286395 3 is in this sequence because (17*10^3 + 67)/3 = 5689 is prime.
%e A286395 Initial terms and associated primes:
%e A286395 a(1) = 1, 79;
%e A286395 a(2) = 3, 5689;
%e A286395 a(3) = 7, 56666689;
%e A286395 a(4) = 8, 566666689;
%e A286395 a(5) = 9, 5666666689; etc.
%t A286395 Select[Range[0, 100000], PrimeQ[(17*10^# + 67)/3] &]
%Y A286395 Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269.
%K A286395 nonn,more,hard
%O A286395 1,2
%A A286395 _Robert Price_, May 09 2017
%E A286395 a(24)-a(26) from _Robert Price_, Jan 24 2019

# Content is available under The OEIS End-User License Agreement: http://oeis.org/LICENSE