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 A202182 #25 Jul 01 2022 09:39:49 %S A202182 1,2,5,15,49,180,715,3081,14217,69905,363926,1996922,1150036,69269925 %N A202182 Number of n-element unlabeled N-free posets. %C A202182 An N-free poset is a poset that does not contain any four elements x, y, z, w such that x is covered by z, y is covered by z, y is covered by w, x||y, x||w, and z||w. - _Salah Uddin Mohammad_, Mar 20 2021 %H A202182 Soheir M. Khamis, <a href="https://doi.org/10.1016/S0012-365X(03)00106-7">Height counting of unlabeled interval and N-free posets</a>, Discrete Math. 275 (2004), no. 1-3, 165-175. %H A202182 Salah Uddin Mohammad, Md. Shah Noor, and Md. Rashed Talukder, <a href="https://cs.uwaterloo.ca/journals/JIS/VOL25/Uddin/uddin6.html">An Exact Enumeration of the Unlabeled Disconnected Posets</a>, J. Int. Seq., Vol. 25 (2022), Article 22.5.4. %e A202182 From _Salah Uddin Mohammad_, Mar 20 2021: (Start) %e A202182 The following poset on 5 nodes is considered to be N-free in this sequence. %e A202182 o o %e A202182 | \ | %e A202182 | o | %e A202182 | \ | %e A202182 o o %e A202182 An alternative definition of N-free used by A003430 excludes this. %e A202182 (End) %Y A202182 Row sums of A202181. %Y A202182 Cf. A003430. %K A202182 nonn,more %O A202182 1,2 %A A202182 _N. J. A. Sloane_, Dec 13 2011 %E A202182 Missing a(12) inserted by _Salah Uddin Mohammad_, Mar 20 2021