%I #23 Jul 13 2023 12:26:49
%S 1,2,3,10,25,29,34,73,76,77,651,884,938,1252,1893,3342,4034,6168,6216,
%T 6231,6812,11046,15448,16628,16918,18734,45935,130393,139289,158819
%N Numbers n such that 5*10^n + 6*R_n + 3 is prime, where R_n = 11...1 is the repunit (A002275) of length n.
%C Also numbers n such that (17*10^n+7)/3 is prime.
%C a(31) > 3*10^5. - _Robert Price_, Jul 13 2023
%H Makoto Kamada, <a href="https://stdkmd.net/nrr/5/56669.htm#prime">Prime numbers of the form 566...669</a>.
%H <a href="/index/Pri#Pri_rep">Index entries for primes involving repunits</a>.
%F a(n) = A101583(n) + 1.
%t Do[ If[ PrimeQ[(17*10^n + 7)/3], Print[n]], {n, 0, 10000}]
%Y Cf. A002275, A101583.
%K more,nonn
%O 1,2
%A _Robert G. Wilson v_, Jan 18 2005
%E a(22)-a(26) from Kamada link by Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 01 2008
%E a(27) from Erik Branger May 01 2013 by _Ray Chandler_, Aug 16 2013
%E a(28)-a(30) from _Robert Price_, Jul 13 2023