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 A133983 #28 Oct 22 2024 07:46:38 %S A133983 1,2,3,8,15,50,119,493,1521,7924,30783,209818 %N A133983 Number of nonisomorphic n-element self-dual posets (or partially ordered sets). %C A133983 Posets whose Hasse diagram looks the same if it is turned upside down. - _N. J. A. Sloane_, Mar 22 2013 %D A133983 R. P. Stanley, Enumerative Combinatorics I, 2nd. ed., p. 247. %o A133983 (Sage) for n in range(1,10): print(len([P for P in Posets(n) if P.is_selfdual()])) # _Jori Mäntysalo_, Oct 02 2014 %Y A133983 Cf. A000112. %K A133983 nonn,more %O A133983 1,2 %A A133983 _Richard Stanley_, Jan 08 2008 %E A133983 a(9) from _Jori Mäntysalo_, Oct 02 2014 %E A133983 a(10-12) from Rico Zöllner and _Konrad Handrich_, Oct 22 2024