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 A102979 Numbers n such that 3*10^n + 8*R_n - 1 is prime, where R_n = 11...1 is the repunit (A002275) of length n. 1

%I

%S 0,1,6,10176,56898

%N Numbers n such that 3*10^n + 8*R_n - 1 is prime, where R_n = 11...1 is the repunit (A002275) of length n.

%C Also numbers n such that (35*10^n-17)/9 is prime.

%C a(6) > 10^5. - _Robert Price_, Mar 30 2015

%H Makoto Kamada, <a href="https://stdkmd.net/nrr/3/38887.htm#prime">Prime numbers of the form 388...887</a>.

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

%F a(n) = A101846(n-1) + 1.

%t Do[ If[ PrimeQ[(35*10^n - 17)/9], Print[n]], {n, 0, 10000}]

%Y Cf. A002275, A101846.

%K more,nonn

%O 1,3

%A _Robert G. Wilson v_, Dec 17 2004

%E Additional term 10176 (a PRP) from _Serge Batalov_, Oct 12 2008

%E Addition of a(5) from Kamada data by _Robert Price_, Dec 13 2010

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Last modified November 29 02:45 EST 2020. Contains 338756 sequences. (Running on oeis4.)