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 A202180 #18 Jun 08 2020 05:24:19 %S A202180 1,1,3,9,31,115,474,2097,9967,50315,268442,1505463,8840306,54169431 %N A202180 Number of n-element unlabeled connected N-free posets. %H A202180 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. %Y A202180 Row sums of A202178 and A202179. %Y A202180 Cf. A003430, A007453, A053554. %K A202180 nonn,more %O A202180 1,3 %A A202180 _N. J. A. Sloane_, Dec 13 2011 %E A202180 Missing term a(12) inserted by _Salah Uddin Mohammad_, May 26 2020