A103051 - OEIS

%I #16 Jan 17 2019 13:44:07

%S 1,2,4,17,25,32,50,74,173,1724,2084,11398

%N Numbers n such that 7*10^n + R_n + 8 is prime, where R_n = 11...1 is the repunit (A002275) of length n.

%C Also numbers n such that (64*10^n+71)/9 is prime.

%C a(13) > 10^5. - _Robert Price_, Sep 21 2015

%H Makoto Kamada, <a href="https://stdkmd.net/nrr/7/71119.htm#prime">Prime numbers of the form 711...119</a>.

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

%F a(n) = A101132(n) + 1.

%t Do[ If[ PrimeQ[(64*10^n + 71)/9], Print[n]], {n, 0, 10000}]

%Y Cf. A002275, A101132.

%K more,nonn

%O 1,2

%A _Robert G. Wilson v_, Jan 19 2005

%E a(12) from Kamada data by _Robert Price_, Dec 14 2010