|
%I #18 Jan 17 2019 13:44:07
%S 2,8,1056,19835,20018,36464,81606
%N Numbers n such that 8*10^n + 5*R_n + 2 is prime, where R_n = 11...1 is the repunit (A002275) of length n.
%C Also numbers n such that (77*10^n+13)/9 is prime.
%C a(8) > 10^5. - _Robert Price_, Oct 25 2015
%H Makoto Kamada, <a href="https://stdkmd.net/nrr/8/85557.htm#prime">Prime numbers of the form 855...557</a>.
%H <a href="/index/Pri#Pri_rep">Index entries for primes involving repunits</a>.
%F a(n) = A101072(n) + 1.
%t Do[ If[ PrimeQ[(77*10^n + 13)/9], Print[n]], {n, 0, 10000}]
%Y Cf. A002275, A101072.
%K more,nonn
%O 1,1
%A _Robert G. Wilson v_, Jan 19 2005
%E a(4)-a(6) from Kamada data by _Robert Price_, Dec 14 2010
%E a(7) from _Robert Price_, Oct 25 2015
| 