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 A263857 #9 Oct 31 2015 14:38:29
%S A263857 1,1,1,1,1,2,1,0,1,1,3,3,2,3,2,0,1,0,0,0,1,1,4,6,6,9,8,7,4,5,2,2,2,3,
%T A263857 0,2,0,0,0,1,0,0,0,0,0,0,0,1
%N A263857 Triangle read by rows: T(n,k) (n>=0, k>=n+1) is the number of posets with n elements and k antichains.
%C A263857 Row sums give A000112.
%H A263857 FindStat - Combinatorial Statistic Finder, <a href="http://www.findstat.org/StatisticsDatabase/St000070">The number of antichains of a poset</a>.
%e A263857 Triangle begins:
%e A263857 1,
%e A263857 1,
%e A263857 1,1,
%e A263857 1,2,1,0,1,
%e A263857 1,3,3,2,3,2,0,1,0,0,0,1,
%e A263857 1,4,6,6,9,8,7,4,5,2,2,2,3,0,2,0,0,0,1,0,0,0,0,0,0,0,1,
%e A263857 ...
%e A263857 The two element poset with 2 incomparable elements x, y has 4 antichains: {}, {x}, {y}, and {x,y}. The two element poset with 2 comparable elements x, y has 3 antichains: {}, {x}, and {y}. So T(2,1) = 1 and T(2,2) = 1.
%Y A263857 Cf. A000112.
%K A263857 nonn,tabf
%O A263857 0,6
%A A263857 _Christian Stump_, Oct 28 2015