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Integers k such that 10^k + 43 is a prime number.
27

%I #27 Aug 30 2021 03:10:06

%S 1,5,37,253,1129,1441,35393

%N Integers k such that 10^k + 43 is a prime number.

%C a(8) > 10^5. - _Robert Price_, Nov 01 2013

%C See Kamada link - primecount.txt for terms, primesize.txt for discovery details including probable or proved primes - search on "10043".

%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=5 is a term because 10^5 + 43 = 100043, which is prime.

%t Select[Range[2*10^3],PrimeQ[10^#+43]&] - _Vladimir Joseph Stephan Orlovsky_, Apr 29 2008

%o (PARI) is(n)=ispseudoprime(10^n+43) \\ _Charles R Greathouse IV_, Apr 28 2015

%Y Cf. A049054, A088274, A088275.

%K nonn,more

%O 1,2

%A Julien Peter Benney (jpbenney(AT)ftml.net), Jun 01 2005

%E a(7)=35393 from _Robert Price_, Mar 16 2010

%E Edited by _Ray Chandler_, Dec 23 2010