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 A368815 #4 Jan 06 2024 23:58:43 %S A368815 0,4,24,104,320,648,1540,2832,3996,7860,12100,15552,25376,35084,36840, %T A368815 62752,81600,97272,131556,163720,178332,245564,296516,336960,421600, %U A368815 497172,557280,678552,786016,836520,1038500,1185344,1301124,1525444,1720740,1893600,2166720,2419612,2628600,2991440 %N A368815 Number of edges in a regular 2n-gon when all vertices are connect by straight lines except for the n lines joining diametrically opposite vertices. %C A368815 See A368813 and A368814 for images of the 2n-gons. %F A368815 a(n) = A368813(n) + A368814(n) - 1 by Euler's formula. %Y A368815 Cf. A368813 (regions), A368814 (vertices), A368816 (k-gons), A368757, A135565. %K A368815 nonn %O A368815 1,2 %A A368815 _Scott R. Shannon_, Jan 06 2024