Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 61st year, we have over 378,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”).
%I #12 May 07 2018 09:53:56
%S 0,2,8,40,240,1992,24416,483040,16343872,982635280,106979975168,
%T 21285548190080,7783083940331520,5254164116114948480,
%U 6577258363669088914432,15332656940815954900371968,66830735142688170751257497600,546722015615195079134707942219904
%N Number of simple graphs with n vertices rooted at a pair of distinguished vertices.
%C The graphs do not need to be connected.
%H Andrew Howroyd, <a href="/A304070/b304070.txt">Table of n, a(n) for n = 1..50</a>
%F a(n) = 2*A304069(n).
%e 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 Cf. A304074 (for connected graphs), A000088 (not rooted).
%K nonn
%O 1,2
%A _Brendan McKay_, May 05 2018
%E Terms a(13) and beyond from _Andrew Howroyd_, May 06 2018