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A280272 Numbers n such that (229*10^n - 1)/3 is prime. 0

%I #12 Jul 10 2020 11:39:09

%S 3,6,8,9,10,17,27,28,45,81,83,225,246,1732,2957,3021,5459,5702,5740,

%T 7924,15110,18683,25149,46968,48944,49571,70122,147699,158339

%N Numbers n such that (229*10^n - 1)/3 is prime.

%C Numbers such that the digits 76 followed by n occurrences of the digit 3 is prime (see Example section).

%C a(30) > 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 763w</a>.

%e 3 is in this sequence because (229*10^3 - 1)/3 = 76333 is prime.

%e Initial terms and primes associated:

%e a(1) = 3, 76333;

%e a(2) = 6, 76333333;

%e a(3) = 8, 7633333333;

%e a(4) = 9, 76333333333;

%e a(5) = 10, 763333333333; etc.

%t Select[Range[0, 100000], PrimeQ[(229*10^# - 1)/3] &]

%o (PARI) is(n)=ispseudoprime((229*10^n - 1)/3) \\ _Charles R Greathouse IV_, Jun 13 2017

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

%K nonn,more,hard

%O 1,1

%A _Robert Price_, Dec 30 2016

%E a(24)-a(29) from _Robert Price_, Jul 10 2020

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Last modified March 29 09:14 EDT 2024. Contains 371268 sequences. (Running on oeis4.)