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 A303831 #27 Sep 23 2019 02:02:11 %S A303831 0,1,3,16,98,879,11260,230505,7949596,483572280,53011686200, %T A303831 10589943940654,3880959679322754,2623201177625659987, %U A303831 3286005731275218388682,7663042204550840483139108,33407704152242477510352455230,273327599183687887638526170380380 %N A303831 Birooted graphs: number of unlabeled connected graphs with n nodes rooted at 2 indistinguishable roots. %H A303831 Andrew Howroyd, <a href="/A303831/b303831.txt">Table of n, a(n) for n = 1..40</a> %H A303831 Jean-François Alcover, <a href="/A303831/a303831.txt">Mathematica program</a> %F A303831 G.f.: B(x)/G(x) - (C(x^2) + C(x)^2)/2 where B(x) is the g.f. of A303829, G(x) is the g.f. of A000088 and C(x) is the g.f. of A126100. - _Andrew Howroyd_, May 03 2018 %F A303831 a(n) = A303830(n) + A304071(n). - _Brendan McKay_, May 05 2018 %t A303831 (* See the links section. *) %Y A303831 Cf. A303829 (not necessarily connected). 3rd column of A304311. %Y A303831 Cf. A000088 (not rooted), A126100 (connected single root), A053506 (2 roots adjacent). %K A303831 nonn %O A303831 1,3 %A A303831 _Brendan McKay_, May 01 2018 %E A303831 a(12)-a(18) from _Andrew Howroyd_, May 03 2018