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 A175863 #15 Feb 25 2024 11:11:24 %S A175863 7,71,379,2659 %N A175863 Numbers k > 1 such that 2^(k-1) == (2*k + 1) (mod k^2). %C A175863 No further terms up to 5 million. - _Harvey P. Dale_, Mar 20 2016 %C A175863 The definition implies 2^(k-1) == 1 (mod k), so all terms are either primes or Sarrus numbers (A001567). There are no further prime terms below 10^12, and no further Sarrus terms below 2^64. - _Lucas A. Brown_, Feb 19 2024 %H A175863 Jan Feitsma, <a href="https://web.archive.org/web/20130316150225/http://www.janfeitsma.nl/math/psp2/index">The pseudoprimes below 2^64</a>. %t A175863 Select[Range[3000],PowerMod[2,#-1,#]==1&&PowerMod[2,#-1,#^2]-1==2*#&] (* _Harvey P. Dale_, Mar 20 2016 *) %Y A175863 Cf. A001567, A128465. %K A175863 nonn,hard,more %O A175863 1,1 %A A175863 _Alzhekeyev Ascar M_, Sep 30 2010