A102974 - OEIS

%I #31 Jan 04 2021 05:05:36

%S 1,6,11,13,19,23,67,108,118,176,673,780,1088,1219,1656,6245,10739,

%T 12590,17513,26000,32544,53274,131784

%N Numbers k such that 3*10^k + 6*R_k - 5 is prime, where R_k = 11...1 is the repunit (A002275) of length k.

%C Also numbers k such that (11*10^k-17)/3 is prime.

%C a(24) > 2*10^5. - _Robert Price_, Jun 10 2018

%H Makoto Kamada, <a href="https://stdkmd.net/nrr/3/36661.htm#prime">Prime numbers of the form 366...661</a>.

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

%F a(n) = A101839(n) + 1.

%t Do[ If[ PrimeQ[(11*10^k - 17)/3], Print[k]], {k, 1, 10000}]

%Y Cf. A002275, A101839.

%K nonn,more

%O 1,2

%A _Robert G. Wilson v_, Dec 17 2004

%E Addition of a(17)-a(20) from Kamada data by _Robert Price_, Dec 10 2010

%E a(21) from Erik Branger May 01 2013 by _Ray Chandler_, Aug 16 2013

%E a(22) from Kamada data by _Robert Price_, Jan 29 2015

%E a(23) from _Robert Price_, Jun 10 2018

%E 0 removed by _Georg Fischer_, Jan 03 2021