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A289943 Numbers k such that (304*10^k - 43)/9 is prime. 0

%I

%S 0,2,3,6,8,9,12,24,39,93,99,147,254,416,510,572,582,1488,1734,5856,

%T 19196,40112

%N Numbers k such that (304*10^k - 43)/9 is prime.

%C For k>0, numbers such that the digits 33 followed by k-1 occurrences of the digit 7 followed by the digit 3 is prime (see Example section).

%C a(23) > 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 337w3.</a>

%e 3 is in this sequence because (304*10^3 - 43)/9 = 33773 is prime.

%e Initial terms and primes associated:

%e a(1) = 0, 29;

%e a(2) = 2, 3373;

%e a(3) = 3, 33773;

%e a(4) = 6, 33777773;

%e a(5) = 8, 3377777773; etc.

%t Select[Range[0, 100000], PrimeQ[(304*10^# - 43)/9] &]

%o (PARI) isok(k) = isprime((304*10^k - 43)/9); \\ _Michel Marcus_, Jul 16 2017

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

%K nonn,more,hard

%O 1,2

%A _Robert Price_, Jul 15 2017

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Last modified January 24 07:18 EST 2020. Contains 331189 sequences. (Running on oeis4.)