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 A132220 #24 Jun 29 2025 09:03:28
%S A132220 1,2,4,10,24,63,166,471,1408,4436,14719,51468,188754,725010,2907576,
%T A132220 12141462,52654529,236584104,1098926868,5266708497,25997964452,
%U A132220 131975740172,688019138485,3678898458587,20153878941460,113000861804642,647866385202660,3794917399892511,22693153274994534,138436809489370914,860962282687080614
%N A132220 Number of line graphs on n unlabeled nodes.
%H A132220 Max Alekseyev, <a href="/A132220/b132220.txt">Table of n, a(n) for n = 1..60</a>
%H A132220 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/LineGraph.html">Line Graph</a>.
%F A132220 For n>=3, a(n) = A000664(n) - A000664(n-3). - _Max Alekseyev_, Sep 03 2016
%t A132220 << Combinatorica`; With[{e = Table[NumberOfGraphs[2 n, n], {n, 12}]}, e - Join[{0, 0, 1}, Drop[e, -3]]] (* _Eric W. Weisstein_, Oct 30 2017 *)
%t A132220 << Combinatorica`; With[{e = Table[Coefficient[GraphPolynomial[2 n, x], x, n], {n, 12}]}, e - Join[{0, 0, 1}, Drop[e, -3]]] (* _Eric W. Weisstein_, Oct 30 2017 *)
%Y A132220 Euler transform of A003089.
%Y A132220 Cf. A132219 (labeled case).
%Y A132220 Cf. A000664.
%K A132220 nonn
%O A132220 1,2
%A A132220 _Vladeta Jovovic_, Aug 14 2007
%E A132220 a(25)-a(60) from _Max Alekseyev_, Sep 07 2016