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 A137814 #19 Aug 23 2023 10:59:36 %S A137814 1,2,3,5,7,11,19,29,47,79,127,191,379 %N A137814 Smallest size of a topology that needs at least n points. %D A137814 M. Erné and K. Stege, Counting finite posets and topologies, Tech. Report 236, University of Hannover, 1990. %H A137814 Swee Hong Chan and Igor Pak, <a href="https://arxiv.org/abs/2308.10214">Computational complexity of counting coincidences</a>, arXiv:2308.10214 [math.CO], 2023. See p. 10. %H A137814 M. Erné and K. Stege, <a href="http://dx.doi.org/10.1007/BF00383446">Counting finite posets and topologies</a>, Order, September 1991, Volume 8, Issue 3, pp 247-265. %H A137814 K. Ragnarsson and B. E. Tenner, <a href="http://dx.doi.org/10.1016/j.jcta.2009.05.002">Obtainable sizes of topologies on finite sets</a>, J. Combin. Theory Ser. A 117 (2010) 138-151. %e A137814 There is no topology with less than 4 points having 7 open sets. However, there do exist topologies on 3 points that have 2, 3, 4, 5, 6 and 8 open sets. %Y A137814 Cf. A137813 and A003064 (smallest number which needs an addition chain of at-least-length n). %K A137814 nonn %O A137814 0,2 %A A137814 _Bridget Tenner_, Feb 11 2008 %E A137814 Name improved and a(0), a(1), a(12) added by _Achim Flammenkamp_, Oct 23 2016