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A178434 Numbers n such that 10^n - 71 is prime. 0

%I

%S 2,3,4,5,7,9,10,14,22,98,127,151,158,274,377,1015,2146,8499,13885,

%T 13991,17834,18211,36271,52317,53804,104212,117059,178695

%N Numbers n such that 10^n - 71 is prime.

%C a(29) > 2.5*10^5. - _Robert Price_, Apr 12 2015

%H Makoto Kamada, <a href="https://stdkmd.net/nrr/aaaba.htm">Near-repdigit numbers of the form AA...AABA</a>.

%H Makoto Kamada, <a href="https://stdkmd.net/nrr/9/99929.htm#prime">Prime numbers of the form 99...9929</a>.

%H <a href="/index/Pri#Pri_rep">Index entries for primes involving repunits</a>.

%e 10^4 - 71 = 9929 which is a prime number.

%t nMax=1000; Do[If[PrimeQ[10^n-71], Print[n]], {n, nMax}]

%o (PARI) is(n)=ispseudoprime(10^n-71) \\ _Charles R Greathouse IV_, Jun 13 2017

%Y Cf. A108330, A108328.

%K more,nonn

%O 1,1

%A _Robert Price_, Dec 21 2010

%E a(24:25)=52317,53804 from _Robert Price_, Apr 25 2011

%E a(26)-a(28) from Kamada data by _Robert Price_, Apr 12 2015

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Last modified November 11 15:46 EST 2019. Contains 329018 sequences. (Running on oeis4.)