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 A367494 #9 Nov 21 2023 08:32:16
%S A367494 1,1,2,7,37,272,2637,32469,493602,9062503,197409097,5027822588,
%T A367494 147896295785,4972353491993,189357434418082,8104194176872583,
%U A367494 387121098095180237,20513320778472547576,1199236185075846230469,76970026071431034905229,5399593095642890354948802
%N A367494 Number of (2+2)-free naturally labeled posets on [n].
%C A367494 A partial order R is naturally labeled if xRy => x<y.
%C A367494 A partial order is (2+2)-free if it does not contain an induced subposet that is isomorphic to the union of two disjoint 2-element chains.
%H A367494 David Bevan, Gi-Sang Cheon, and Sergey Kitaev, <a href="https://arxiv.org/abs/2311.08023">On naturally labelled posets and permutations avoiding 12-34</a>, arXiv:2311.08023 [math.CO], 2023.
%e A367494 a(3) = A006455(3) = 7: {}, {1R2}, {1R3}, {2R3}, {1R2, 1R3}, {1R3, 2R3}, {1R2, 1R3, 2R3}.
%e A367494 a(4) = A006455(4) - 3 = 37: {1R2, 3R4}, {1R3, 2R4} and {1R4, 2R3} (trivially) contain a 2+2 subposet.
%Y A367494 Cf. A006455 (naturally labeled posets), A113226 ({3,2+2}-free naturally labeled posets).
%K A367494 nonn
%O A367494 0,3
%A A367494 _David Bevan_, Nov 20 2023