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 A007903 #44 Jun 01 2023 13:57:50 %S A007903 2,4,11,60,877,42944,7339704 %N A007903 The number of distinct principal ideals in the semigroup of binary relations on an n-set. %C A007903 a(n) is the number of Green's J-classes in the semigroup of binary relations on an n-set. - _James Mitchell_, May 10 2015 %D A007903 K. H. Kim, Boolean Matrix Theory and Applications, Marcel Decker Inc., 1982. %D A007903 George Markowsky, 1991; Markowsky and Breen, 1993; Breen, 1995. %H A007903 Jin Bai Kim, <a href="http://www.koreascience.or.kr/article/JAKO198311919478487.page">Tables of D-classes in the semigroup Bn of the binary relations on a set X with n-elements</a>, Bull. Korean Math. Soc., Volume 20, Issue 1, 1983, pp. 9-13. %H A007903 Wikipedia, <a href="http://en.wikipedia.org/wiki/Green%27s_relations">Green's relations</a> %H A007903 <a href="/index/Se#semigroups">Index entries for sequences related to semigroups</a> %F A007903 a(n) is asymptotic to 2^(n^2)/n!^2 (from Kim reference). - _Geoffrey Critzer_, May 14 2023 %Y A007903 Cf. A173311. %K A007903 nonn,hard,more,nice %O A007903 1,1 %A A007903 Michael A Breen (MAB1699(AT)tntech.edu)