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 A228551 #25 Jan 22 2020 16:27:39 %S A228551 1,1,2,12,146,2820,79682,3109932,163268786,11373086100,1049057429762, %T A228551 128748967088412,21220651011079346,4747770003765805380, %U A228551 1456585782002699624642,6390825031791150383749864 %N A228551 Number of connected labeled graded posets on n vertices. %C A228551 Here 'graded' is to be intended as in A001833. %H A228551 David A. Klarner, <a href="https://doi.org/10.1016/S0021-9800(69)80100-6">The number of graded partially ordered sets</a>, Journal of Combinatorial Theory, vol.6, no.1, pp.12-19, (January-1969). %F A228551 E.g.f.: 1 + log(F(x)), where F(x) is the e.g.f. of A001833. %Y A228551 Cf. A001833. %K A228551 nonn %O A228551 0,3 %A A228551 _Daniele P. Morelli_, Aug 25 2013