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%I #17 Jan 17 2019 13:44:07
%S 30,41,228,581,1290,2580,3696,11390,21558
%N Numbers n such that 9*10^n + 4*R_n - 1 is prime, where R_n = 11...1 is the repunit (A002275) of length n.
%C Also numbers n such that (85*10^n-13)/9 is prime.
%C a(10) > 10^5. - _Robert Price_, Nov 05 2015
%H Makoto Kamada, <a href="https://stdkmd.net/nrr/9/94443.htm#prime">Prime numbers of the form 944...443</a>.
%H <a href="/index/Pri#Pri_rep">Index entries for primes involving repunits</a>.
%F a(n) = A101007(n) + 1.
%t Do[ If[ PrimeQ[(85*10^n - 13)/9], Print[n]], {n, 0, 10000}]
%Y Cf. A002275, A101007.
%K more,nonn
%O 1,1
%A _Robert G. Wilson v_, Jan 19 2005
%E a(8)-a(9) from Kamada data by _Robert Price_, Dec 14 2010
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