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Joseph O'Rourke
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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 through no other point of $Q$. So points block visibility, and the only points visible from the origin are those with a clear line of sight:
   LatticeVisib8Grid
Let $\nu(n)$ be the ratio of the number of points visible within the square with corner $(n,n)$ to $n^2$. For example, for $n=8$, $43$ of the $64$ points are visible, so $\nu(n) = 43/64 \approx 0.67$.

Q: What is $\lim_{n \to \infty} \nu(n)$?

It appears to be approaching $\approx 0.614$:
   LatticeVisib80Plot
The question bears some similarity to Polya's Orchard Problem (T.T. Allen, "Polya's orchard problem," The American Mathematical Monthly 93(2): 98-104 (1986). Jstor link), but I cannot see my question is answered in that literature.

One could ask the same question for $\mathbb{Z}^d$.


**Answered** by Pete Clark: the limit is $\frac{1}{\zeta(d)}$. Thus in higher dimensions, almost all the lattice points are visible (because $\zeta(d)$ approaches $1$).

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 through no other point of $Q$. So points block visibility, and the only points visible from the origin are those with a clear line of sight:
   LatticeVisib8Grid
Let $\nu(n)$ be the ratio of the number of points visible within the square with corner $(n,n)$ to $n^2$. For example, for $n=8$, $43$ of the $64$ points are visible, so $\nu(n) = 43/64 \approx 0.67$.

Q: What is $\lim_{n \to \infty} \nu(n)$?

It appears to be approaching $\approx 0.614$:
   LatticeVisib80Plot
The question bears some similarity to Polya's Orchard Problem (T.T. Allen, "Polya's orchard problem," The American Mathematical Monthly 93(2): 98-104 (1986). Jstor link), but I cannot see my question is answered in that literature.

One could ask the same question for $\mathbb{Z}^d$.

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 through no other point of $Q$. So points block visibility, and the only points visible from the origin are those with a clear line of sight:
   LatticeVisib8Grid
Let $\nu(n)$ be the ratio of the number of points visible within the square with corner $(n,n)$ to $n^2$. For example, for $n=8$, $43$ of the $64$ points are visible, so $\nu(n) = 43/64 \approx 0.67$.

Q: What is $\lim_{n \to \infty} \nu(n)$?

It appears to be approaching $\approx 0.614$:
   LatticeVisib80Plot
The question bears some similarity to Polya's Orchard Problem (T.T. Allen, "Polya's orchard problem," The American Mathematical Monthly 93(2): 98-104 (1986). Jstor link), but I cannot see my question is answered in that literature.

One could ask the same question for $\mathbb{Z}^d$.


**Answered** by Pete Clark: the limit is $\frac{1}{\zeta(d)}$. Thus in higher dimensions, almost all the lattice points are visible (because $\zeta(d)$ approaches $1$).
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Joseph O'Rourke
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Joseph O'Rourke
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  • 958

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 through no other point of $Q$. So points block visibility, and the only points visible from the origin are those with a clear line of sight:
   LatticeVisib8Grid
Let $\nu(n)$ be the ratio of the number of points visible within the square with corner $(n,n)$ to $n^2$. For example, for $n=8$, $43$ of the $64$ points are visible, so $\nu(n) = 43/64 \approx 0.67$.

Q: What is $\lim_{n \to \infty} \nu(n)$?

It appears to be approaching $\approx 0.614$:
   LatticeVisib80Plot
The question bears some similarity to Polya's Orchard Problem (T.T. Allen, "Polya's orchard problem," The American Mathematical Monthly 93(2): 98-104 (1986). Jstor link), but I cannot see my question is answered in that literature.

One could ask the same question for $\mathbb{Z}^d$.

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 through no other point of $Q$. So points block visibility, and the only points visible from the origin are those with a clear line of sight:
   LatticeVisib8Grid
Let $\nu(n)$ be the ratio of the number of points visible within the square with corner $(n,n)$ to $n^2$. For example, for $n=8$, $43$ of the $64$ points are visible, so $\nu(n) = 43/64 \approx 0.67$.

Q: What is $\lim_{n \to \infty} \nu(n)$?

It appears to be approaching $\approx 0.614$:
   LatticeVisib80Plot
The question bears some similarity to Polya's Orchard Problem (T.T. Allen, "Polya's orchard problem," The American Mathematical Monthly 93(2): 98-104 (1986). Jstor link), but I cannot see my question is answered in that literature.

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 through no other point of $Q$. So points block visibility, and the only points visible from the origin are those with a clear line of sight:
   LatticeVisib8Grid
Let $\nu(n)$ be the ratio of the number of points visible within the square with corner $(n,n)$ to $n^2$. For example, for $n=8$, $43$ of the $64$ points are visible, so $\nu(n) = 43/64 \approx 0.67$.

Q: What is $\lim_{n \to \infty} \nu(n)$?

It appears to be approaching $\approx 0.614$:
   LatticeVisib80Plot
The question bears some similarity to Polya's Orchard Problem (T.T. Allen, "Polya's orchard problem," The American Mathematical Monthly 93(2): 98-104 (1986). Jstor link), but I cannot see my question is answered in that literature.

One could ask the same question for $\mathbb{Z}^d$.

Source Link
Joseph O'Rourke
  • 150.8k
  • 36
  • 358
  • 958
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