|
%I #8 May 19 2024 21:55:02
%S 0,1,3,7,13,18,19,36,78,129,171,175,237,607,619,717,954,1386,3948,
%T 7939,16519,17686,18759,19986,36340,39547,44014,60579,170842
%N Numbers k such that (58*10^k + 221)/9 is prime.
%C For k > 1, numbers k such that the digit 6 followed by k-2 occurrences of the digit 4 followed by the digits 69 is prime (see Example section).
%C a(30) > 5*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 64w69</a>.
%e 3 is in this sequence because (58*10^3 + 221)/9 = 6469 is prime.
%e Initial terms and associated primes:
%e a(1) = 0, 31;
%e a(2) = 1, 89;
%e a(3) = 3, 6469;
%e a(4) = 7, 64444469;
%e a(5) = 13, 64444444444469; etc.
%t Select[Range[0, 100000], PrimeQ[(58*10^# + 221)/9] &]
%Y Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269.
%K nonn,more,hard
%O 1,3
%A _Robert Price_, Aug 28 2017
|
