|
%I #19 Jan 17 2019 13:44:07
%S 1,4,7,34,82,451,772,2554,6250,15137,20074,37378,53068
%N Numbers n such that 7*10^n + 4*R_n + 5 is prime, where R_n = 11...1 is the repunit (A002275) of length n.
%C Also numbers n such that (67*10^n+41)/9 is prime.
%C a(14) > 10^5. - _Robert Price_, Sep 27 2015
%H Makoto Kamada, <a href="https://stdkmd.net/nrr/7/74449.htm#prime">Prime numbers of the form 744...449</a>.
%H <a href="/index/Pri#Pri_rep">Index entries for primes involving repunits</a>.
%F a(n) = A101142(n) + 1.
%t Do[ If[ PrimeQ[(67*10^n + 41)/9], Print[n]], {n, 0, 10000}]
%Y Cf. A002275, A101142.
%K more,nonn
%O 1,2
%A _Robert G. Wilson v_, Jan 19 2005
%E a(10)-a(11) from Kamada data by _Robert Price_, Dec 14 2010
%E a(12) from Erik Branger May 01 2013 by _Ray Chandler_, Aug 16 2013
%E a(13) from _Robert Price_, Sep 27 2015
| 