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%I #21 Jan 17 2019 13:44:07
%S 1,2,4,25,58,148,373,421,1915,3746,16784,30050,60026,93346
%N Numbers n such that 9*10^n + 4*R_n + 3 is prime, where R_n = 11...1 is the repunit (A002275) of length n.
%C Also numbers n such that (85*10^n+23)/9 is prime.
%C a(15) > 10^5. - _Robert Price_, Nov 14 2015
%H Makoto Kamada, <a href="https://stdkmd.net/nrr/9/94447.htm#prime">Prime numbers of the form 944...447</a>.
%H <a href="/index/Pri#Pri_rep">Index entries for primes involving repunits</a>.
%F a(n) = A101008(n) + 1.
%t Do[ If[ PrimeQ[(85*10^n + 23)/9], Print[n]], {n, 0, 10000}]
%o (PARI) is(n)=isprime(9*10^n + 4*(10^n-1)/9 + 3) \\ _Anders Hellström_, Nov 14 2015
%Y Cf. A002275, A101008.
%K more,nonn
%O 1,2
%A _Robert G. Wilson v_, Jan 19 2005
%E a(11) from Kamada data by _Robert Price_, Dec 14 2010
%E a(12) from Erik Branger May 01 2013 by _Ray Chandler_, Aug 17 2013
%E a(13)-a(14) from _Robert Price_, Nov 14 2015
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