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A102947 Numbers n such that 2*10^n-3 is prime. 2

%I #23 Jan 17 2019 13:44:07

%S 1,2,3,4,13,14,76,237,872,988,1280,1370,2686,3612,4051,4645,9162,

%T 10856,25959,64882,144220,153746,185930

%N Numbers n such that 2*10^n-3 is prime.

%C Numbers n such that 10^n + 8*R_n - 2 is prime, where R_n = 11...1 is the repunit (A002275) of length n.

%C a(21) > 10^5. - _Robert Price_, Nov 16 2014

%C a(24) > 2*10^5. - _Robert Price_, Jul 11 2015

%H Makoto Kamada, <a href="https://stdkmd.net/nrr/1/19997.htm#prime">Prime numbers of the form 199...997</a>.

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

%F a(n) = A102034(n) + 1.

%t Do[ If[ PrimeQ[2*10^n - 3], Print[n]], {n, 0, 10000}]

%o (PARI) is(n)=ispseudoprime(2*10^n-3) \\ _Charles R Greathouse IV_, Jun 06 2017

%Y Cf. A102034.

%K more,nonn

%O 1,2

%A _Robert G. Wilson v_, Dec 16 2004

%E Addition of a(18)-a(20) from Kamada data by _Robert Price_, Dec 09 2010

%E a(21)-a(23) from _Robert Price_, Jul 11 2015

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Last modified March 29 06:15 EDT 2024. Contains 371265 sequences. (Running on oeis4.)