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49 votes
4 answers
4k views

What fraction of the integer lattice can be seen from the origin?

Consider the integer lattice points in the positive quadrant $Q$ of $\mathbb{Z}^2$. Say that a point $(x,y)$ of $Q$ is visible from the origin if the segment from $(0,0)$ to $(x,y) \in Q$ passes ...
Joseph O'Rourke's user avatar
11 votes
1 answer
499 views

Tiling with incommensurate triangles

Say that two triangles are incommensurate if they do not share an edge length or a vertex angle, and their areas differ. Suppose you'd like to tile the plane with pairwise incommensurate triangles. I ...
Joseph O'Rourke's user avatar
41 votes
2 answers
2k views

Can we find lattice polyhedra with faces of area 1,2,3,...?

I asked this question two months ago on MSE, where it earned the rare Tumbleweed badge for garnering zero votes, zero answers, and 25 views over 61 days. Perhaps justifiably so! Here I repeat it with ...
Joseph O'Rourke's user avatar
3 votes
1 answer
366 views

Illumination from visible lattice points with inverse square intensity

It is well known that the number of $\mathbb{Z}^2$ lattice points visible from the origin is $6/\pi^2$, about $61$%. See, e.g., What fraction of the integer lattice can be seen from the origin?. I am ...
Joseph O'Rourke's user avatar