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