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 A128241 #10 Aug 15 2019 16:59:01 %S A128241 0,1,2,11,41,220,1243,9368,89049,1135894,19381407,445505570, %T A128241 13741579905,566739127723,31124921885829 %N A128241 Number of n-node (unlabeled) connected graphs with girth 4. %F A128241 a(n) = A024607(n) - A126757(n). - _Martin Fuller_, May 01 2015 %Y A128241 Cf. A024607, A126757. %Y A128241 Cf. A128041, A128042, A128236-A128243. %K A128241 nonn,more %O A128241 3,3 %A A128241 _Keith Briggs_, May 05 2007 %E A128241 Corrected and extended by _Martin Fuller_, May 01 2015