OFFSET
1,3
COMMENTS
Permutations of the 3 points are not counted separately.
EXAMPLE
The triangle begins:
0
1 4
4 10 22
10 21 42 76
20 39 70 120 186
35 65 112 184 279 412
56 100 166 264 390 566 772
.
a(2) = T(1,2) = 1, because the grid points on the two longer sides of the rectangle are collinear: (0,0) (0,1) (0,2) and (1,0) (1,1) (2,2).
a(3) = T(2,2) = 4, because there are 8 triples of collinear points:
(0,0) (0,1) (0,2),
(0,0) (1,0) (2,0),
(0,0) (1,1) (2,2),
(0,1) (1,1) (2,1),
(0,2) (1,1) (2,0),
(0,2) (1,2) (2,2),
(1,0) (1,1) (1,2),
(2,0) (2,1) (2,2).
CROSSREFS
KEYWORD
nonn,tabl
AUTHOR
Hugo Pfoertner, Oct 15 2018
STATUS
approved