This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A109137 #20 Oct 17 2024 05:50:52 %S A109137 2,14,42,144,200,302,7242,8718,10568,24438,41734 %N A109137 Numbers k such that k * (10^k - 1) + 1 is prime. %C A109137 Larger values certified with ECM. No more up to 6000. %o A109137 (PARI) is(n)=ispseudoprime(n*(10^n-1)+1) \\ _Charles R Greathouse IV_, Jun 13 2017 %o A109137 (Python) %o A109137 from sympy import isprime %o A109137 def afind(limit, startk=1): %o A109137 k, pow10 = startk, 10**startk %o A109137 for k in range(startk, limit+1): %o A109137 if isprime(k*(pow10 - 1) + 1): print(k, end=", ") %o A109137 k += 1 %o A109137 pow10 *= 10 %o A109137 afind(500) # _Michael S. Branicky_, Aug 26 2021 %Y A109137 Cf. A110807. %K A109137 more,nonn %O A109137 1,1 %A A109137 _Jason Earls_, Aug 18 2005 %E A109137 a(7)-a(8) from _Ryan Propper_, Sep 20 2006 %E A109137 a(9) from _Michael S. Branicky_, Aug 26 2021 %E A109137 a(10) from _Michael S. Branicky_, Apr 05 2023 %E A109137 a(11) from _Michael S. Branicky_, Oct 17 2024