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 A381471 #7 Mar 05 2025 15:08:17
%S A381471 1,1,2,3,7,13,63,838
%N A381471 Number of non-isomorphic Dynkin systems on n points.
%C A381471 A Dynkin system on a set S is a subset of the power set of S which contains the empty set, is closed under complements in S, and is closed under union of disjoint sets.
%H A381471 Martin Rubey and Peter Taylor, <a href="https://mathoverflow.net/q/405736/46140">What is the number of finite Dynkin systems?</a>, MathOverflow.
%H A381471 Wikipedia, <a href="https://en.wikipedia.org/wiki/Dynkin_system">Dynkin system</a>
%F A381471 a(n) >= A000041(n).
%e A381471 The a(3) = 3 representative systems are:
%e A381471 {{}, {1,2,3}}
%e A381471 {{}, {1}, {2,3}, {1,2,3}}
%e A381471 {{}, {1}, {2}, {3}, {1,2}, {1,3}, {2,3}, {1,2,3}}
%Y A381471 Cf. A000041, A380571 (labeled case).
%K A381471 nonn,more
%O A381471 0,3
%A A381471 _Andrew Howroyd_, Feb 26 2025