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A337701
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 vertices in that figure.
4
9, 12, 15, 18, 49, 56, 252, 280, 308, 312, 650, 700, 1845, 1968, 2091, 1962, 3401, 3580, 7056, 7392, 7728, 7560, 11050, 11492, 19305, 20020, 20735, 19320, 27497, 28384, 43164, 44472, 45780, 45720, 57794, 59356, 84357, 86520, 88683, 86730, 108145, 110660
OFFSET
3,1
COMMENTS
Because of symmetry, a(n) is divisible by n.
See A337700 for illustrations.
LINKS
FORMULA
a(n) = A337702(n) - A337700(n) by Euler's formula, there being 1 hole.
CROSSREFS
KEYWORD
nonn
AUTHOR
Lars Blomberg, Sep 16 2020
STATUS
approved