A103033 - OEIS

%I #22 Oct 26 2023 11:45:38

%S 1,3,4,5,6,10,13,58,96,178,360,420,455,1008,1517,2975,3999,5425,10819,

%T 16036,32076,47237,111385,190935

%N Numbers n such that 6*10^n + 3*R_n + 4 is prime, where R_n = 11...1 is the repunit (A002275) of length n.

%C Also numbers n such that (19*10^n+11)/3 is prime.

%C a(25) > 3*10^5. - _Robert Price_, Oct 26 2023

%H Makoto Kamada, <a href="https://stdkmd.net/nrr/6/63337.htm#prime">Prime numbers of the form 633...337</a>.

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

%F a(n) = A101526(n) + 1.

%t Do[ If[ PrimeQ[(19*10^n + 11)/3], Print[n]], {n, 0, 10000}]

%Y Cf. A002275, A101526.

%K more,nonn

%O 1,2

%A _Robert G. Wilson v_, Jan 18 2005

%E Addition of a(19)-a(20) from Kamada data by _Robert Price_, Dec 10 2010

%E a(21)-a(22) from Erik Branger May 01 2013 by _Ray Chandler_, Aug 16 2013

%E a(23)-a(24) from _Robert Price_, Oct 26 2023