|
%I #11 Dec 25 2019 23:11:20
%S 0,1,2,3,9,11,13,15,17,24,37,44,48,58,65,104,393,413,1265,2292,2620,
%T 3037,3628,5159,5629,12809,18572,26875,29695,32267,34277,43621,138768
%N Numbers k such that (28*10^k + 173)/3 is prime.
%C For k>1, numbers n such that the digit 9 followed by k-2 occurrences of the digit 3 followed by the digits 91 is prime (see Example section).
%C a(34) > 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/primedifficulty.txt">Search for 93w91</a>.
%e 3 is in this sequence because (28*10^3 + 173)/3 = 9391 is prime.
%e Initial terms and primes associated:
%e a(1) = 0, 67;
%e a(2) = 1, 151;
%e a(3) = 2, 991;
%e a(4) = 3, 9391;
%e a(5) = 9, 9333333391, etc.
%t Select[Range[0, 100000], PrimeQ[(28*10^# + 173)/3] &]
%o (PARI) is(n)=ispseudoprime((28*10^n + 173)/3) \\ _Charles R Greathouse IV_, Jun 13 2017
%Y Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269.
%K nonn,more
%O 1,3
%A _Robert Price_, May 02 2016
%E a(33) from _Robert Price_, Dec 25 2019
|
