A283448 - OEIS

%I #17 Jun 10 2024 23:36:26

%S 1,2,3,5,14,18,38,65,217,218,342,560,648,962,1151,2043,2113,2641,5738,

%T 13295,15793,20424,35729,48474,62298,88077

%N Numbers k such that (265*10^k + 11)/3 is prime.

%C For k > 1, numbers k such that the digits 88 followed by k-1 occurrences of the digit 3 followed by the digit 7 is prime (see Example section).

%C a(27) > 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 883w7</a>.

%e 3 is in this sequence because (265*10^3 + 11)/3 = 88337 is prime.

%e Initial terms and associated primes:

%e a(1) = 1, 887;

%e a(2) = 2, 8837;

%e a(3) = 3, 88337;

%e a(4) = 5, 8833337;

%e a(5) = 14, 8833333333333337; etc.

%t Select[Range[0, 100000], PrimeQ[(265*10^# + 11)/3] &]

%o (PARI) isok(n) = isprime((265*10^n + 11)/3); \\ _Indranil Ghosh_, Mar 09 2017

%Y Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269.

%K nonn,more,hard

%O 1,2

%A _Robert Price_, Mar 07 2017