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A018811 Number of lines through exactly 4 points of an n X n grid of points. 2
0, 0, 0, 0, 10, 4, 4, 20, 44, 36, 64, 124, 200, 236, 272, 308, 548, 692, 852, 1108, 1396, 1452, 1768, 2116, 2496, 2908, 3568, 4292, 5428, 5956, 6500, 7444, 8452, 8980, 10208, 11516, 13348, 14700, 16116, 17596, 20124, 22476, 24956, 28092, 31404, 33052, 36032 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,5

LINKS

Seiichi Manyama, Table of n, a(n) for n = 0..1000

S. Mustonen, On lines and their intersection points in a rectangular grid of points [From Seppo Mustonen, Apr 18 2009]

FORMULA

a(n) = 1/2 (f(n, 5) - 2 f(n, 4) + f(n, 3)) where f(n, k) = Sum ((n - |kx|)(n - |ky|)); -n<kx<n, -n<ky<n, (x, y)=1. [From Seppo Mustonen, Apr 18 2009]

CROSSREFS

Cf. A119437.

Sequence in context: A081986 A063566 A153690 * A309707 A100844 A076587

Adjacent sequences:  A018808 A018809 A018810 * A018812 A018813 A018814

KEYWORD

nonn

AUTHOR

David W. Wilson

STATUS

approved

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Last modified October 22 09:56 EDT 2019. Contains 328315 sequences. (Running on oeis4.)