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%I #10 Sep 16 2020 12:51:07
%S 21,28,35,42,112,128,567,630,693,720,1417,1526,3930,4192,4454,4302,
%T 7163,7540,14700,15400,16100,16008,22900,23816,39771,41244,42717,
%U 40800,56482,58304,88341,91018,93695,94176,118067,121258,171912,176320,180728,178626
%N Place two n-gons with radii 1 and 2 concentrically, forming an annular area between them. Connect all the vertices with line segments that lie entirely within that area. Then a(n) is the number of edges in that figure.
%C Because of symmetry, a(n) is divisible by n.
%C See A337700 for illustrations.
%H Lars Blomberg, <a href="/A337702/b337702.txt">Table of n, a(n) for n = 3..102</a>
%F a(n) = A337700(n) + A337701(n) by Euler's formula, there being 1 hole.
%Y Cf. A337700, A337701, A337703.
%K nonn
%O 3,1
%A _Lars Blomberg_, Sep 16 2020
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