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A102986 Numbers n such that 4*10^n + 2*R_n + 5 is prime, where R_n = 11...1 is the repunit (A002275) of length n. 1

%I #22 Jan 17 2019 13:44:07

%S 1,4,136,181,325,3292,3871,4690,7876,11911,16096,21649,43045

%N Numbers n such that 4*10^n + 2*R_n + 5 is prime, where R_n = 11...1 is the repunit (A002275) of length n.

%C Also numbers n such that (38*10^n+43)/9 is prime.

%C a(14) > 10^5. - _Robert Price_, May 08 2015

%H Makoto Kamada, <a href="https://stdkmd.net/nrr/4/42227.htm#prime">Prime numbers of the form 422...227</a>.

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

%F a(n) = A101721(n) + 1.

%t Do[ If[ PrimeQ[(38*10^n + 43)/9], Print[n]], {n, 0, 10000}]

%Y Cf. A002275, A101721.

%K more,nonn

%O 1,2

%A _Robert G. Wilson v_, Jan 17 2005

%E Addition of a(10)-a(12) from Kamada data by _Robert Price_, Dec 13 2010

%E a(13) from Erik Branger, May 01 2013, submitted by _Ray Chandler_, Aug 16 2013

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Last modified March 28 05:39 EDT 2024. Contains 371235 sequences. (Running on oeis4.)