A102959 - OEIS

%I #19 Jan 17 2019 13:44:07

%S 1,4,34,36,42,52,163,208,216,1417,14646,22794,25648,32515,51421

%N Numbers n such that 2*10^n + 7*R_n + 2 is prime, where R_n = 11...1 is the repunit (A002275) of length n.

%C Also numbers n such that (25*10^n+11)/9 is prime.

%C a(16) > 10^5. - _Robert Price_, Mar 12 2015

%H Makoto Kamada, <a href="https://stdkmd.net/nrr/2/27779.htm#prime">Prime numbers of the form 277...779</a>.

%H <a href="/index/Pri#Pri_rep">Index entries for primes involving repunits</a>.

%F a(n) = A101968(n) + 1.

%t Do[ If[ PrimeQ[(25*10^n + 11)/9], Print[n]], {n, 0, 10000}]

%Y Cf. A002275, A101968.

%K more,nonn

%O 1,2

%A _Robert G. Wilson v_, Dec 17 2004

%E a(11)-a(13) from Kamada data by _Robert Price_, Dec 14 2010

%E a(14) from Erik Branger May 01 2013 by _Ray Chandler_, Aug 16 2013

%E a(15) from _Robert Price_, Mar 12 2015