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

Search: id:a281171
Showing 1-1 of 1

%I A281171 #11 Jun 07 2024 23:59:15
%S A281171 1,2,5,9,13,20,21,32,33,56,73,81,149,313,455,753,1013,1166,1304,1679,
%T A281171 15758,15896,21801,41353,45421,131090,151007
%N A281171 Numbers k such that (5*10^k + 37)/3 is prime.
%C A281171 For k > 1, numbers k such that the digit 1 followed by k-2 occurrences of the digit 6 followed by the digits 79 is prime (see Example section).
%C A281171 a(28) > 2*10^5.
%H A281171 Makoto Kamada, <a href="https://stdkmd.net/nrr">Factorization of near-repdigit-related numbers</a>.
%H A281171 Makoto Kamada, <a href="https://stdkmd.net/nrr/prime/prime_difficulty.txt">Search for 16w79</a>.
%e A281171 2 is in this sequence because (5*10^2 + 37) / 3 = 179 is prime.
%e A281171 Initial terms and associated primes:
%e A281171 a(1) = 1, 29;
%e A281171 a(2) = 2, 179;
%e A281171 a(3) = 5, 166679;
%e A281171 a(4) = 9, 1666666679;
%e A281171 a(5) = 13, 16666666666679; etc.
%t A281171 Select[Range[0, 100000], PrimeQ[(5*10^# + 37) / 3] &]
%Y A281171 Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269.
%K A281171 nonn,more,hard
%O A281171 1,2
%A A281171 _Robert Price_, Jan 16 2017
%E A281171 a(26)-a(27) from _Robert Price_, Mar 02 2018

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