A102936 - OEIS

%I #17 Jul 08 2021 03:08:55

%S 1,3,6,15,70,76,13024,60346

%N Numbers k such that 10^k + 5*R_k - 2 is prime, where R_k = 11...1 is the repunit (A002275) of length k.

%C Also numbers k such that (14*10^k - 23)/9 is prime.

%C a(9) > 10^5. - _Robert Price_, Apr 10 2015

%H Makoto Kamada, <a href="https://stdkmd.net/nrr/1/15553.htm#prime">Prime numbers of the form 155...553</a>.

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

%F a(n) = A102019(n) + 1.

%t Do[ If[ PrimeQ[(14*10^n - 23)/9], Print[n]], {n, 0, 10000}]

%Y Cf. A002275, A102019.

%K more,nonn

%O 1,2

%A _Robert G. Wilson v_, Dec 16 2004

%E Addition of a(7) from Kamada data by _Robert Price_, Dec 13 2010

%E a(8) from _Robert Price_, Apr 10 2015