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%I #16 Apr 06 2023 08:30:09
%S 2,14,42,144,200,302,7242,8718,10568,24438
%N Numbers k such that k * (10^k - 1) + 1 is prime.
%C Larger values certified with ECM. No more up to 6000.
%o (PARI) is(n)=ispseudoprime(n*(10^n-1)+1) \\ _Charles R Greathouse IV_, Jun 13 2017
%o (Python)
%o from sympy import isprime
%o def afind(limit, startk=1):
%o k, pow10 = startk, 10**startk
%o for k in range(startk, limit+1):
%o if isprime(k*(pow10 - 1) + 1): print(k, end=", ")
%o k += 1
%o pow10 *= 10
%o afind(500) # _Michael S. Branicky_, Aug 26 2021
%Y Cf. A110807.
%K more,nonn
%O 1,1
%A _Jason Earls_, Aug 18 2005
%E a(7)-a(8) from _Ryan Propper_, Sep 20 2006
%E a(9) from _Michael S. Branicky_, Aug 26 2021
%E a(10) from _Michael S. Branicky_, Apr 05 2023
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