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%I #25 Jan 17 2019 13:44:07
%S 1,7,133,938,17666,20864,56756
%N Numbers n such that 7*10^n + R_n + 2 is prime, where R_n = 11...1 is the repunit (A002275) of length n.
%C Also numbers n such that (64*10^n+17)/9 is prime.
%C a(8) > 10^5. - _Robert Price_, Sep 18 2015
%H Makoto Kamada, <a href="https://stdkmd.net/nrr/7/71113.htm#prime">Prime numbers of the form 711...113</a>.
%H <a href="/index/Pri#Pri_rep">Index entries for primes involving repunits</a>.
%F a(n) = A101131(n) + 1.
%t Do[ If[ PrimeQ[(64*10^n + 17)/9], Print[n]], {n, 0, 10000}]
%o (PARI) is(n)=isprime((64*10^n + 17)/9) \\ _Anders Hellström_, Sep 18 2015
%Y Cf. A002275, A101131.
%K more,nonn
%O 1,2
%A _Robert G. Wilson v_, Jan 19 2005
%E a(5)-a(6) from Kamada data by _Robert Price_, Dec 14 2010
%E a(7) from _Robert Price_, Sep 18 2015
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