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Integers k such that 5*10^k + 51 is prime.
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%I #20 Dec 28 2023 23:30:15

%S 1,3,4,16,430,727,1415,2691,3160,3904,5464,19875,65255,68524

%N Integers k such that 5*10^k + 51 is prime.

%C See Kamada link - primecount.txt for terms, primesize.txt for discovery details including probable or proved primes - search on "50051".

%C a(15) > 10^5. - _Robert Price_, Jan 28 2017

%H Makoto Kamada, <a href="https://stdkmd.net/nrr/prime/">List of near-repdigit-related prime numbers</a>.

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

%e k = 4 is a member because: 5*10^4+51 = 5*10000+51 = 50000+51 = 50051, which is prime.

%t Select[Range[1, 1000], PrimeQ[5*10^# + 51] &] (* _Julien Kluge_, Dec 15 2016 *)

%Y Cf. A049054, A088274, A088275, A095688, A107083, A108049, A108050, A108052, A108054.

%K more,nonn

%O 1,2

%A Julien Peter Benney (jpbenney(AT)ftml.net), Oct 04 2005

%E a(11)-a(12) from _Ray Chandler_, Dec 23 2010

%E Prepended a(1)=1 by _Robert Price_, Jan 28 2017

%E a(13)-a(14) from _Robert Price_, Jan 28 2017