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A337702
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.
4
21, 28, 35, 42, 112, 128, 567, 630, 693, 720, 1417, 1526, 3930, 4192, 4454, 4302, 7163, 7540, 14700, 15400, 16100, 16008, 22900, 23816, 39771, 41244, 42717, 40800, 56482, 58304, 88341, 91018, 93695, 94176, 118067, 121258, 171912, 176320, 180728, 178626
OFFSET
3,1
COMMENTS
Because of symmetry, a(n) is divisible by n.
See A337700 for illustrations.
LINKS
FORMULA
a(n) = A337700(n) + A337701(n) by Euler's formula, there being 1 hole.
CROSSREFS
KEYWORD
nonn
AUTHOR
Lars Blomberg, Sep 16 2020
STATUS
approved