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 A367565 #14 Nov 27 2023 10:29:40
%S A367565 1,3,32,1863,1316515,75868099847
%N A367565 Number of reduced contexts on n labeled objects.
%C A367565 Equivalently, number of set systems on n points such that each of the systems obtained from the corresponding closure system on n points by omitting all intersections of other sets in the system and the set {1,...,n}; the systems with all sets shared at least one common element are not allowed.
%C A367565 This is the labeled version of A047684.
%D A367565 B. Ganter and R. Wille, Formal Concept Analysis, Springer-Verlag, 1999, ISBN 3-540-62771-5, p. 24.
%D A367565 B. Ganter and S. A. Obiedkov, Conceptual Exploration, Springer 2016, ISBN 978-3-662-49290-1, pages 1-315.
%H A367565 Dmitry I. Ignatov, <a href="http://arxiv.org/abs/1703.02819">Introduction to Formal Concept Analysis and Its Applications in Information Retrieval and Related Fields</a>, arXiv:1703.02819 [cs.IR], 2017; RuSSIR 2014, 42-141.
%H A367565 Dmitry I. Ignatov, <a href="https://github.com/dimachine/ReducedContexts/">Supporting iPython code for counting reduced contexts up to n=6 objects</a>, Github repository.
%H A367565 Wikipedia, <a href="https://en.wikipedia.org/wiki/Formal_concept_analysis">Formal Concept Analysis</a>.
%e A367565 The a(2)=3 set systems are {{1},{2}}, {{},{1}}, and {{},{2}}. The corresponding formal contexts represented by crosstables are
%e A367565 1 x. 1 .x 1 ..
%e A367565 2 .x 2 .. 2 x. .
%Y A367565 A047684 (unlabeled version), A102896 (all closure systems).
%K A367565 nonn,hard,more
%O A367565 1,2
%A A367565 _Dmitry I. Ignatov_, Nov 23 2023