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%I #17 Jan 17 2019 13:44:07
%S 1,3,19,109,129,280,387,447,487,1048,3298,3460,9454,26103,61693,66469
%N Numbers n such that 5*10^n + R_n + 2 is a prime, where R_n = 11...1 is the repunit (A002275) of length n.
%C Also numbers n such that (46*10^n+17)/9 is a prime.
%C a(17) > 10^5. - _Robert Price_, Jun 20 2015
%H Makoto Kamada, <a href="https://stdkmd.net/nrr/5/51113.htm#prime">Prime numbers of the form 511...113</a>.
%H <a href="/index/Pri#Pri_rep">Index entries for primes involving repunits</a>.
%F a(n) = A101570(n) + 1.
%t Do[ If[ PrimeQ[(46*10^n + 17)/9], Print[n]], {n, 0, 10000}]
%Y Cf. A002275, A101570.
%K more,nonn
%O 1,2
%A _Robert G. Wilson v_, Jan 18 2005
%E Addition of a(14) from Kamada data by _Robert Price_, Dec 12 2010
%E a(15)-a(16) from _Robert Price_, Jun 20 2015