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 A081712 #12 Sep 18 2023 22:48:00 %S A081712 4,6,7,8,10,20,21,26,101,119,172,409,621,1043,1204,1283,1673,2003, %T A081712 4336,5773,12913,13517 %N A081712 Numbers k such that k! - k# + 1 is prime, where k# is the primorial function. %C A081712 Some of the larger entries may only correspond to probable primes. %H A081712 Mike Oakes, <a href="http://groups.yahoo.com/group/primenumbers/message/12028">Primo-factorials</a>. %H A081712 Mike Oakes, <a href="/A081710/a081710.txt">Primo-factorials</a>, message 12028 in primenumbers Yahoo group, Apr 3, 2003. [Cached copy] %H A081712 Joe McLean, <a href="http://web.archive.org/web/20091027034731/http://uk.geocities.com/nassarawa%40btinternet.com/probprim2.htm">Interesting Sources of Probable Primes</a>. %e A081712 a(1)=4 because 4!-4#+1=19 is prime %Y A081712 Cf. A081710, A081711, A081713. %K A081712 nonn,more,hard %O A081712 1,1 %A A081712 _Mike Oakes_, Apr 04 2003 %E A081712 More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 03 2008 %E A081712 Offset corrected by _Sean A. Irvine_, Sep 18 2023