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 A189771 #7 Feb 16 2025 08:33:14 %S A189771 0,0,0,0,0,1,2,7,20,76,334,2498,36398,1225629,89060804,12978995815, %T A189771 3646305137905,1947685504386516,1969840087225045340, %U A189771 3770491704215436784514,13674048211165798257589446,94122727377410134768239226418 %N A189771 Number of simple graphs on n nodes that are Euler (all nodes even) but not Eulerian (single cycle passes through all edges). %C A189771 There are more Euler graphs than Eulerian graphs since there exist disconnected graphs having multiple disjoint cycles with each node even but for which no single cycle passes through all edges. %H A189771 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/EulerGraph.html">Euler Graph</a> %H A189771 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/EulerianGraph.html">Eulerian Graph</a> %F A189771 a(n) = A002854(n) - A133736(n). %Y A189771 Cf. A002854, A133736. %K A189771 nonn %O A189771 1,7 %A A189771 _Eric W. Weisstein_, Apr 26 2011