A103038 - OEIS

%I #20 Jan 17 2019 13:44:07

%S 0,1,3,4,10,22,40,54,81,84,106,193,597,681,1363,1876,4024,14163,18733,

%T 20842,23728,26419,31450,44694,64767

%N Numbers n such that 6*10^n + 5*R_n - 4 is prime, where R_n = 11...1 is the repunit (A002275) of length n.

%C Also numbers n such that (59*10^n-41)/9 is prime.

%C a(26) > 10^5. - _Robert Price_, Sep 11 2015

%H Makoto Kamada, <a href="https://stdkmd.net/nrr/6/65551.htm#prime">Prime numbers of the form 655...551</a>.

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

%F a(n) = A101531(n-1) + 1 for n>1.

%t Do[ If[ PrimeQ[(59*10^n - 41)/9], Print[n]], {n, 0, 10000}]

%Y Cf. A002275, A101531.

%K more,nonn

%O 1,3

%A _Robert G. Wilson v_, Jan 18 2005

%E a(18)-a(22) from Kamada data by _Robert Price_, Dec 14 2010

%E a(23)-a(24) from Erik Branger May 01 2013 by _Ray Chandler_, Aug 16 2013

%E Inserted a(1)=0 by _Robert Price_, Sep 11 2015

%E a(25) from _Robert Price_, Sep 11 2015