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 A062587 #44 Jul 04 2021 07:53:06 %S A062587 2,19,41,43,337,479,9127,37549,44017,59971,128327,176191,193601 %N A062587 Numbers k such that 21^k - 20^k is prime. %C A062587 Terms greater than 1000 may correspond to (unproven) strong pseudoprimes. %H A062587 <a href="http://www.primenumbers.net/prptop/searchform.php?form=21%5Ep-20%5Ep">Top probable primes of the form 21^p-20^p</a> %o A062587 (PARI) is(n)=ispseudoprime(21^n-20^n) \\ _Charles R Greathouse IV_, Jun 13 2017 %Y A062587 Cf. A000043, A057468, A059801, A059802, A062572-A062666. %K A062587 nonn,hard %O A062587 1,1 %A A062587 _Mike Oakes_, May 18 2001, May 19 2001 %E A062587 a(8) from _Jean-Louis Charton_, Feb 29 2012 %E A062587 a(9) and a(10) from _Robert Price_, May 30 2012 %E A062587 Edited by _M. F. Hasler_, Sep 16 2013 %E A062587 a(11) added by _Jean-Louis Charton_, Nov 24 2014 %E A062587 a(12) added by _Jean-Louis Charton_, Feb 05 2015 %E A062587 a(13) added by _Jean-Louis Charton_, Feb 18 2015