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 A128237 #7 Aug 15 2019 16:58:21 %S A128237 0,1,3,15,59,296,1604,11303,102108,1250114,20738069,467523871, %T A128237 14230096759,581439661069,31720637440030 %N A128237 Number of n-node (unlabeled) graphs with girth 4. %F A128237 a(n) = A006785(n) - A006787(n). %Y A128237 Cf. A006785, A006787. %Y A128237 Cf. A128041, A128042, A128236-A128243. %K A128237 nonn %O A128237 3,3 %A A128237 _Keith Briggs_, May 05 2007 %E A128237 Corrected and extended by _Martin Fuller_, May 01 2015