|
%I #19 Jul 08 2021 01:36:50
%S 36,183,330,393,17520,27222
%N Numbers k such that 2*10^k + R_k + 6 is prime, where R_k = 11...1 is the repunit (A002275) of length k.
%C Also numbers k such that (19*10^k + 53)/9 is prime.
%C a(7) > 10^5. - _Robert Price_, Feb 07 2015
%H Makoto Kamada, <a href="https://stdkmd.net/nrr/2/21117.htm#prime">Prime numbers of the form 211...117</a>.
%H <a href="/index/Pri#Pri_rep">Index entries for primes involving repunits</a>.
%F a(n) = A101954(n) + 1.
%t Do[ If[ PrimeQ[(19*10^n + 53)/9], Print[n]], {n, 0, 10000}]
%Y Cf. A002275, A101954.
%K more,nonn
%O 1,1
%A _Robert G. Wilson v_, Dec 17 2004
%E Addition of a(5)-a(6) from Kamada data by _Robert Price_, Dec 13 2010
| 