cp's OEIS Frontend

A276353 Numbers k such that (19*10^k + 77) / 3 is prime.

%I A276353 #19 May 26 2024 16:03:59
%S A276353 1,2,3,5,6,17,22,56,71,90,93,109,124,135,179,255,1804,2541,2707,3195,
%T A276353 4952,5884,9301,19847,27903,45739,65545,69424,103907,160619,168173,
%U A276353 297497,299640
%N A276353 Numbers k such that (19*10^k + 77) / 3 is prime.
%C A276353 For k > 1, numbers k such that the digit 6 followed by k-2 occurrences of the digit 3 followed by the digits 59 is prime (see Example section).
%C A276353 a(34) > 3*10^5.
%H A276353 Makoto Kamada, <a href="https://stdkmd.net/nrr">Factorization of near-repdigit-related numbers</a>.
%H A276353 Makoto Kamada, <a href="https://stdkmd.net/nrr/prime/prime_difficulty.txt">Search for 63w59</a>.
%e A276353 3 is in this sequence because (19*10^3 + 77) / 3 = 6359 is prime.
%e A276353 Initial terms and associated primes:
%e A276353 a(1) = 1, 89;
%e A276353 a(2) = 2, 659
%e A276353 a(3) = 3, 6359;
%e A276353 a(4) = 5, 633359;
%e A276353 a(5) = 6, 6333359, etc.
%t A276353 Select[Range[0, 100000], PrimeQ[(19*10^# + 77) / 3] &]
%o A276353 (PARI) is(n)=ispseudoprime((19*10^n + 77)/3) \\ _Charles R Greathouse IV_, Jun 13 2017
%Y A276353 Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269.
%K A276353 nonn,more
%O A276353 1,2
%A A276353 _Robert Price_, Aug 31 2016
%E A276353 a(29)-a(31) from _Robert Price_, May 28 2019
%E A276353 a(32)-a(33) from _Robert Price_, Jun 01 2023