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A211382 Number of intersections of diagonals in the exterior of a regular n-gon. 1
0, 0, 0, 0, 7, 24, 63, 110, 242, 360, 650, 812, 1425, 1680, 2737, 2718, 4788, 5200, 7812, 8272, 12075, 11328, 17875, 18486, 25542, 26264, 35438 (list; graph; refs; listen; history; text; internal format)
OFFSET

3,5

LINKS

Table of n, a(n) for n=3..29.

Bjorn Poonen; Michael Rubinstein, The Number of Intersection Points Made by the Diagonals of a Regular Polygon, SIAM J. Discrete Mathematics 11 (1998), nr. 1, pp. 135-156; doi: 10.1137/S0895480195281246; arXiv: math.MG/9508209.

Eric Weisstein, Regular Polygon Division by Diagonals (MathWorld).

FORMULA

a(n) = 1/24*n*(n-3)*(n-5)*(2*n-11) for n odd

CROSSREFS

Cf. A006561.

Sequence in context: A002969 A029585 A114291 * A217746 A211381 A305676

Adjacent sequences:  A211379 A211380 A211381 * A211383 A211384 A211385

KEYWORD

nonn,more

AUTHOR

Martin Renner, Feb 07 2013

EXTENSIONS

a(17)-a(29) from Martin Renner, Feb 24 2013

STATUS

approved

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Last modified December 11 18:19 EST 2019. Contains 329925 sequences. (Running on oeis4.)