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 A057186 #40 Mar 10 2025 13:04:15 %S A057186 5,79,89,709,797,1163,6971,140053,177967,393257,463511 %N A057186 Numbers k such that (20^k+1)/21 is a prime. %C A057186 (20^1163+1)/21, a 1512-digit number, has been certified prime with Primo. - _Rick L. Shepherd_, May 17 2002 %H A057186 Paul Bourdelais, <a href="https://listserv.nodak.edu/cgi-bin/wa.exe?A2=NMBRTHRY;417ab0d6.0906">A Generalized Repunit Conjecture</a>. %H A057186 H. Dubner and T. Granlund, <a href="https://cs.uwaterloo.ca/journals/JIS/VOL3/DUBNER/dubner.html">Primes of the Form (b^n+1)/(b+1)</a>, J. Integer Sequences, 3 (2000), #P00.2.7. %o A057186 (PARI) forprime(n=3,10^7, if( ispseudoprime((20^n+1)/21), print1(n,", "))); \\ _Joerg Arndt_, May 26 2013 %K A057186 nonn %O A057186 1,1 %A A057186 _N. J. A. Sloane_, Sep 15 2000 %E A057186 a(8) from _Paul Bourdelais_, Apr 06 2010 %E A057186 a(9) from _Paul Bourdelais_, May 26 2013 %E A057186 a(10), corresponding to a probable prime, from _Paul Bourdelais_, Dec 08 2014 %E A057186 a(11) from _Paul Bourdelais_, Mar 10 2025