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A275096 Numbers n such that 2*10^n + 89 is prime. 0

%I

%S 1,3,4,8,9,10,13,20,27,74,89,93,137,139,296,310,662,749,1249,2540,

%T 2848,3309,8677,11573,15286,17125,39526,42187,44476,47823,92897

%N Numbers n such that 2*10^n + 89 is prime.

%C For n>1, numbers n such that the digit 2 followed by n-2 occurrences of the digit 0 followed by the digits 89 is prime (see Example section).

%C a(32) > 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 20w89.</a>

%e 3 is in this sequence because 2*10^3 + 89 = 2089 is prime.

%e Initial terms and associated primes:

%e a(1) = 1, 109;

%e a(2) = 3, 2089;

%e a(3) = 4, 20089;

%e a(4) = 8, 200000089;

%e a(5) = 9, 2000000089, etc.

%t Select[Range[0, 100000], PrimeQ[2*10^# + 89] &]

%o (MAGMA) [n: n in [1..500] | IsPrime(2*10^n+89)]; // _Vincenzo Librandi_, Jul 17 2016

%o (PARI) is(n)=ispseudoprime(2*10^n+89) \\ _Charles R Greathouse IV_, Jun 13 2017

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

%K nonn,more

%O 1,2

%A _Robert Price_, Jul 16 2016

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Last modified February 23 16:23 EST 2020. Contains 332177 sequences. (Running on oeis4.)