%I
%S 0,2,3,12,18,23,57,128,543,584,833,2450,2810,2873,3671,6384,10296,
%T 16704,53049,56544,74253
%N Numbers n such that 2*10^n + R_n is prime, where R_n = 11...1 is the repunit (A002275) of length n.
%C Also numbers n such that (19*10^n1)/9 is prime.
%H Makoto Kamada, <a href="https://stdkmd.net/nrr/2/21111.htm#prime">Prime numbers of the form 211...11</a>.
%H <a href="/index/Pri#Pri_rep">Index entries for primes involving repunits</a>
%t Do[ If[ PrimeQ[ 2*10^n + (10^n1)/9], Print[n]], {n, 0, 10000}]
%Y Cf. A002275, A068814.
%K nonn
%O 1,2
%A _Robert G. Wilson v_, Aug 10 2000
%E 6384 from _Hugo Pfoertner_, Oct 16 2004
%E 10296 and 16704 from Ray Chandler, Sep 2010
%E 0 added by _Arkadiusz Wesolowski_, Mar 10 2011
%E 53049 and 56544 from Serge Batalov, Mar 2009 confirmed as next terms by _Ray Chandler_, Feb 03 2012
%E 74253 from _Ray Chandler_, Feb 03 2012
