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 A054920 #23 Mar 17 2020 19:31:33
%S A054920 2,4,68,2592,278796,95720106,111891292036,457846756500066,
%T A054920 6664787020904248568,349363873490889302878250,
%U A054920 66602024342830108271942323060,46557190064705399729526041154647820
%N A054920 Number of connected unlabeled reflexive relations with n nodes such that complement is also connected.
%H A054920 Andrew Howroyd, <a href="/A054920/b054920.txt">Table of n, a(n) for n = 1..50</a>
%H A054920 V. A. Liskovets, <a href="http://www.cs.uwaterloo.ca/journals/JIS/VOL3/LISK/Derseq.html">Some easily derivable sequences</a>, J. Integer Sequences, 3 (2000), #00.2.2.
%F A054920 a(n) = 2*A054919(n) - A000595(n).
%t A054920 A000595 = Import["https://oeis.org/A000595/b000595.txt", "Table"][[All, 2]];
%t A054920 (* EulerInvTransform is defined in A022562 *)
%t A054920 A054919 = Join[{1}, EulerInvTransform[A000595 // Rest]];
%t A054920 a[n_] := 2 A054919[[n + 1]] - A000595[[n + 1]];
%t A054920 Array[a, 50] (* _Jean-François Alcover_, Sep 01 2019, updated Mar 17 2020 *)
%Y A054920 Cf. A000595, A054919.
%K A054920 nonn,easy
%O A054920 1,1
%A A054920 _N. J. A. Sloane_, May 24 2000
%E A054920 More terms from _Vladeta Jovovic_, Jul 17 2000