A103019 - OEIS

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

%S 2,6,9,27,30,48,141,150,372,422,1097,3570,4607,5289,10734,11550,32604,

%T 42470,46311,67578

%N Numbers n such that 5*10^n + 7*R_n - 6 is prime, where R_n = 11...1 is the repunit (A002275) of length n.

%C Also numbers n such that (52*10^n-61)/9 is prime.

%C a(21) > 10^5. - _Robert Price_, Sep 05 2015

%H Makoto Kamada, <a href="https://stdkmd.net/nrr/5/57771.htm#prime">Prime numbers of the form 577...771</a>.

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

%F a(n) = A101584(n) + 1.

%t Do[ If[ PrimeQ[(52*10^n - 61)/9], Print[n]], {n, 0, 10000}]

%Y Cf. A002275, A101584.

%K more,nonn

%O 1,1

%A _Robert G. Wilson v_, Jan 18 2005

%E Addition of a(15)-a(16) from Kamada data by _Robert Price_, Dec 12 2010

%E a(17)-a(19) from Erik Branger May 01 2013 by _Ray Chandler_, Aug 16 2013

%E a(20) from _Robert Price_, Sep 05 2015