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A282278 Numbers k such that (22*10^k + 161)/3 is prime. 0

%I

%S 0,1,2,4,5,6,7,13,28,36,40,74,233,425,828,888,1970,2119,2338,2971,

%T 3030,14005,20190,29589,47034,47292,51457,64326,70259,90110

%N Numbers k such that (22*10^k + 161)/3 is prime.

%C For k>1, numbers such that the digit 7 followed by k-2 occurrences of the digit 3 followed by the digits 87 is prime (see Example section).

%C a(31) > 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 73w87.</a>

%e 4 is in this sequence because (22*10^4 + 161)/3 = 73387 is prime.

%e Initial terms and primes associated:

%e a(1) = 0, 61;

%e a(2) = 1, 127;

%e a(3) = 2, 787;

%e a(4) = 4, 73387;

%e a(5) = 5, 733387; etc.

%t Select[Range[0, 100000], PrimeQ[(22*10^# + 161)/3] &]

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

%K nonn,more,hard

%O 1,3

%A _Robert Price_, Feb 10 2017

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Last modified March 26 20:47 EDT 2019. Contains 321535 sequences. (Running on oeis4.)