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 A323875 #23 Feb 26 2019 05:02:48
%S A323875 0,1,3,19,230,5098,207536,15891372,2343580752,675458276144,
%T A323875 383306076989440,430041136692146912,956431386434331323776,
%U A323875 4224539434553753578497024,37106501188130085159785113344,648740172906485727983524271405824,22591360806791558877526051411343415296,1567817808096346724727108606144936617617408
%N A323875 Number of labeled graphs on n nodes with two connected components.
%D A323875 F. Harary and E. M. Palmer, Graphical Enumeration, Academic Press, 1973, section 1.2.
%H A323875 Marko Riedel et al., <a href="https://math.stackexchange.com/questions/3094635/">Proof of recurrence relation.</a>
%H A323875 Marko Riedel, <a href="/A323875/a323875.maple.txt">Maple implementation of memoized recurrence.</a>
%F A323875 a(n) = A143543(n, 2).
%F A323875 E.g.f.: log(Sum_{q>=0} 2^binomial(q, 2)*z^q/q!)^2/2!.
%Y A323875 Cf. A143543, A323876, A323877.
%K A323875 nonn
%O A323875 1,3
%A A323875 _Marko Riedel_, Feb 05 2019