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A146213 Draw lines through the vertices of a regular n-gon. a(n) is the number of intersection points outside of the n-gon. 2
0, 0, 5, 18, 49, 88, 198, 300, 550, 588, 1235, 1414, 2415, 2576, 4284, 3708, 7068, 7280, 11025, 11330, 16445, 14592, 23650, 23972, 32994, 33208, 44863, 34830, 59675, 59808, 77880, 78064, 99960, 92844, 126429, 126426, 157833, 157560, 194750 (list; graph; refs; listen; history; text; internal format)
OFFSET

3,3

COMMENTS

Note that n divides a(n). For odd n, it appears that a(n)=n(2n^3-15^2+34n-21)/24.

LINKS

Jon E. Schoenfield, Table of n, a(n) for n = 3..100

FORMULA

a(n) = A146212(n) - A007569(n).

CROSSREFS

Sequence in context: A256539 A109363 A218214 * A176145 A270978 A272512

Adjacent sequences:  A146210 A146211 A146212 * A146214 A146215 A146216

KEYWORD

nonn

AUTHOR

T. D. Noe, Oct 28 2008

EXTENSIONS

More terms from Jon E. Schoenfield, Nov 11 2008

STATUS

approved

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Last modified November 15 19:54 EST 2018. Contains 317240 sequences. (Running on oeis4.)