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%I #12 May 25 2024 19:38:58
%S 0,5,8,9,12,39,68,78,98,200,218,359,1064,1127,1355,2868,4940,7236,
%T 12050,24708,47214,52683
%N Numbers k such that (436*10^k - 13)/9 is prime.
%C For k > 1, numbers k such that the digits 48 followed by k-1 occurrences of the digit 4 followed by the digit 3 is prime (see Example section).
%C a(23) > 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 484w3</a>.
%e 5 is in this sequence because (436*10^5 - 13)/9 = 4844443 is prime.
%e Initial terms and associated primes:
%e a(1) = 0, 47;
%e a(2) = 5, 4844443;
%e a(3) = 8, 4844444443;
%e a(4) = 9, 48444444443;
%e a(5) = 12, 48444444444443; etc.
%t Select[Range[0, 100000], PrimeQ[(436*10^# - 13)/9] &]
%Y Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269.
%K nonn,more,hard
%O 1,2
%A _Robert Price_, Oct 19 2017