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 A257562 #34 Jan 21 2020 12:29:36 %S A257562 1,1,2,6,21,79,310,1251,5150,21517,90921,387595,1663936,7183750, %T A257562 31158310,135661904,592558096,2595232344,11392504426,50109205789, %U A257562 220777103354,974162444028,4303957562319,19036842605855,84285643628790,373502845338552,1656428550764640,7351106011540209,32643855249507805,145040974005303590,644756480385363800 %N A257562 Number of permutations of length n that avoid the patterns 4123, 4231, and 4312. %C A257562 G.f. conjectured to be non-D-finite (see Albert et al. link). _Jay Pantone_, Oct 01 2015 %C A257562 Unlike A061552, whose g.f. is also conjectured to be non-D-finite, thousands of terms of the counting sequence are known. - _David Callan_, Aug 29 2017 %H A257562 Jay Pantone, <a href="/A257562/b257562.txt">Table of n, a(n) for n = 0..5000</a> %H A257562 D. Callan, T. Mansour, <a href="http://arxiv.org/abs/1705.00933">Enumeration of small Wilf classes avoiding 1324 and two other 4-letter patterns</a>, arXiv:1705.00933 [math.CO] (2017). %H A257562 David Callan, Toufik Mansour, Mark Shattuck, <a href="https://doi.org/10.1515/puma-2015-0031">Enumeration of permutations avoiding a triple of 4-letter patterns is almost all done</a>, Pure Mathematics and Applications (2019) Vol. 28, Issue 1, 14-69. %H A257562 Michael H. Albert, Cheyne Homberger, Jay Pantone, Nathaniel Shar, Vincent Vatter, <a href="http://arxiv.org/abs/1510.00269">Generating Permutations with Restricted Containers</a>, arXiv:1510.00269 [math.CO], (2015). %e A257562 a(4) = 21 because there are 24 permutations of length 4 and 3 of them do not avoid 4123, 4231, and 4312. %Y A257562 Cf. A053614, A106228, A165542, A165545, A257561, A257562. %K A257562 nonn %O A257562 0,3 %A A257562 _Jay Pantone_, Apr 30 2015