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 A304070 #12 May 07 2018 09:53:56 %S A304070 0,2,8,40,240,1992,24416,483040,16343872,982635280,106979975168, %T A304070 21285548190080,7783083940331520,5254164116114948480, %U A304070 6577258363669088914432,15332656940815954900371968,66830735142688170751257497600,546722015615195079134707942219904 %N A304070 Number of simple graphs with n vertices rooted at a pair of distinguished vertices. %C A304070 The graphs do not need to be connected. %H A304070 Andrew Howroyd, <a href="/A304070/b304070.txt">Table of n, a(n) for n = 1..50</a> %F A304070 a(n) = 2*A304069(n). %e A304070 a(3)=8: 1 for the graph with no edge, 3 for the graph with one edge, 3 for the graph with two edges, 1 for the triangle. %Y A304070 Cf. A304074 (for connected graphs), A000088 (not rooted). %K A304070 nonn %O A304070 1,2 %A A304070 _Brendan McKay_, May 05 2018 %E A304070 Terms a(13) and beyond from _Andrew Howroyd_, May 06 2018