A173502 Number of concave kites (darts or arrowheads) on an n X n grid (or geoboard).

0, 0, 8, 64, 292, 916, 2344, 5048, 10096, 18296, 31400, 50752, 79308, 118876, 173768, 246096, 342256, 465064, 622904, 818552, 1063756, 1361564, 1725432, 2159384, 2682944, 3298568, 4027776, 4873600

Offset

1,3

Links

Table of n, a(n) for n=1..28.

Nathaniel Johnston, C program for computing terms

Example

a(1) = 0, since there is only one point on a 1 X 1 grid.
a(2) = 0, since the four points on a 2 X 2 grid build a convex quadrilateral.
a(3) = 8, since there are two possible forms of darts on a 3 X 3 grid, each can appear in four rotations.

Crossrefs

Cf. A189412, A189417.

Sequence in context: A189265 A167239 A236554 * A223670 A189618 A189690

Adjacent sequences: A173499 A173500 A173501 * A173503 A173504 A173505

Keyword

nonn

Author

Martin Renner, Apr 29 2011

Extensions

a(7)-a(28) from Nathaniel Johnston, Apr 29 2011

Status

approved