cp's OEIS Frontend

A269797 Numbers k such that (29*10^k + 91)/3 is prime.

%I A269797 #20 May 31 2024 22:11:24
%S A269797 1,2,3,4,8,11,18,27,39,54,55,65,75,83,111,164,189,191,204,252,322,371,
%T A269797 449,646,678,754,1641,5210,7787,11691,13682,15994,22356,29203,35756,
%U A269797 57834,64027,72985,74276,104071,219124
%N A269797 Numbers k such that (29*10^k + 91)/3 is prime.
%C A269797 For k > 1, numbers k such that digit 9 followed by k-2 occurrences of digit 6 followed by the digits 97 is prime (see Example section).
%C A269797 a(42) > 3*10^5.
%H A269797 Makoto Kamada, <a href="https://stdkmd.net/nrr/prime/prime_difficulty.txt">Search for 96w97</a>.
%e A269797 6 is in this sequence because (266*10^n+1)/3 = 88666667 is prime.
%e A269797 Initial terms and associated primes:
%e A269797 a(1) = 1, 127,
%e A269797 a(2) = 2, 997,
%e A269797 a(3) = 3, 9697,
%e A269797 a(4) = 4, 96697,
%e A269797 a(5) = 8, 966666697,
%e A269797 a(6) = 11, 966666666697,
%e A269797 a(7) = 18, 9666666666666666697,
%e A269797 a(8) = 27, 9666666666666666666666666697,
%e A269797 a(9) = 39, 9666666666666666666666666666666666666697, etc.
%t A269797 Select[Range[0, 100000], PrimeQ[(29*10^# + 91)/3] &]
%o A269797 (PARI) isok(n) = isprime((29*10^n + 91)/3); \\ _Michel Marcus_, Mar 05 2016
%Y A269797 Cf. A056654, A268448, A269303.
%K A269797 nonn,more
%O A269797 1,2
%A A269797 _Robert Price_, Mar 05 2016
%E A269797 a(40) from _Robert Price_, Apr 12 2020
%E A269797 a(41) from _Robert Price_, May 31 2023