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%I #16 Jan 17 2019 13:44:07
%S 1,22,925,2340,15955,16098,55512,82752
%N Numbers n such that 4*10^n + 7*R_n - 6 is prime, where R_n = 11...1 is the repunit (A002275) of length n.
%C Also numbers n such that (43*10^n-61)/9 is prime.
%C a(9) > 10^5. - _Robert Price_, Jun 01 2015
%H Makoto Kamada, <a href="https://stdkmd.net/nrr/4/47771.htm#prime">Prime numbers of the form 477...771</a>.
%H <a href="/index/Pri#Pri_rep">Index entries for primes involving repunits</a>.
%F a(n) = A101732(n) + 1.
%t Do[ If[ PrimeQ[(43*10^n - 61)/9], Print[n]], {n, 0, 10000}]
%Y Cf. A002275, A101732.
%K more,nonn
%O 1,2
%A _Robert G. Wilson v_, Jan 17 2005
%E Two more PRP terms from _Serge Batalov_, Feb 15 2009
%E a(7)-a(8) from _Robert Price_, Jun 01 2015
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