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 A318987 #18 Oct 27 2019 14:28:46 %S A318987 1,0,3,17,153,1687,26397,1596113,3682361420 %N A318987 Number of semigroups of order n without identity. %H A318987 <a href="/index/Se#semigroups">Index entries for sequences related to semigroups</a> %F A318987 a(n) = A027851(n) - A058129(n). %Y A318987 Cf. A027851, A058129. %K A318987 nonn,more %O A318987 0,3 %A A318987 _Steve Szabo_, Sep 06 2018 %E A318987 More terms from _Joerg Arndt_, Dec 09 2018 %E A318987 a(0) prepended by _Jianing Song_, Oct 26 2019