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A275236 Numbers n such that (28*10^n-97)/3 is prime. 0

%I

%S 1,5,8,20,27,56,74,81,107,217,294,326,525,645,667,764,863,1885,1961,

%T 2913,3056,3192,3327,5480,8455,22797,50147,89141,96265

%N Numbers n such that (28*10^n-97)/3 is prime.

%C For n>1, numbers n such that the digit 9 followed by n-2 occurrences of the digit 3 followed by the digits 01 is prime (see Example section).

%C a(30) > 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 93w01.</a>

%e 5 is in this sequence because (28*10^5-97)/3 = 877 is prime.

%e Initial terms and primes associated:

%e a(1) = 1, 61;

%e a(2) = 5, 933301;

%e a(3) = 8, 933333301;

%e a(4) = 20, 933333333333333333301;

%e a(5) = 27, 9333333333333333333333333301, etc.

%t Select[Range[0, 100], PrimeQ[(28*10^#-97)/3 && # > 0] &] (* Corrected by _Georg Fischer_, Jul 22 2019 *)

%o (PARI) is(n)=ispseudoprime((28*10^n-97)/3) \\ _Charles R Greathouse IV_, Jul 21 2016

%o (MAGMA) [n: n in [1..500] | IsPrime((28*10^n-97) div 3)]; // _Vincenzo Librandi_, Jul 21 2016

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

%K nonn,more

%O 1,2

%A _Robert Price_, Jul 20 2016

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Last modified September 20 20:02 EDT 2020. Contains 337265 sequences. (Running on oeis4.)