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 A281723 #14 Jan 25 2024 11:44:11 %S A281723 2,2,3,4,7,13,17,59,253,979 %N A281723 Smallest positive integer that cannot be obtained as the number of linear extensions of a poset of size n. %C A281723 a(n) is the smallest positive integer such that A160371(a(n)) > n. %H A281723 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. 12. %H A281723 Swee Hong Chan and Igor Pak, <a href="https://arxiv.org/abs/2401.09723">Linear extensions and continued fractions</a>, arXiv:2401.09723 [math.CO], 2024. %e A281723 a(8) = 253, so the number 253 cannot be obtained as the number of linear extensions of a poset of size 8, but every integer from 1 to 252 can. %Y A281723 Cf. A160371. %K A281723 nonn,hard,more %O A281723 0,1 %A A281723 _François Labelle_, Jan 28 2017