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 A318590 #41 Jan 29 2025 11:23:15 %S A318590 1,1,2,5,28,177,1982,33997,1020516,54570672,5347070228,967135763525, %T A318590 324200029119318,202046821340636691,234878262433630160622, %U A318590 511060736355598412146405,2088401066728281847415734793,16079824271822965645002329491423,233994776259866281916838227225733732 %N A318590 Number of connected balanced simple signed graphs on n unlabeled nodes. %H A318590 Andrew Howroyd, <a href="/A318590/b318590.txt">Table of n, a(n) for n = 0..50</a> %H A318590 Wikipedia, <a href="https://en.wikipedia.org/wiki/Signed_graph">Signed graph</a> %F A318590 a(2*n+1) = A054921(2*n+1)/2, a(2*n) = (a(n) + A054919(n) + A054921(2*n) - A054921(n))/2. %F A318590 Inverse Euler transform of A034892. %Y A318590 Cf. A005142, A034892, A053465, A054919, A054921. %K A318590 nonn %O A318590 0,3 %A A318590 _Andrew Howroyd_, Sep 25 2018