Eisensteins Everywhere

Looking at a random direction from the origin, what is the probability that your line of sight doesn't encounter an Eisenstein integer (that is, the probability that a line from the origin at a random direction does not intersect any Eisenstein integer)?

If the probability is P , P, submit your answer as 1000 P \lfloor 1000P \rfloor .

Notes:

  • An Eisenstein integer is a complex number of the form a + b ω , a+b\omega, where ω = 1 + i 3 2 \displaystyle \omega = \frac{-1+i\sqrt{3}}{2} and a a and b b are both integers. For example, 1 , ω 1, \omega and 3 + 2 ω 3+2\omega are all Eisenstein integers.

  • \lfloor \cdot \rfloor denotes the floor function .


Inspiration .


The answer is 1000.

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1 solution

Wen Z
Oct 10, 2016

By definition, there exists a surjection from the set N 2 \mathbb{N}^2 to the set of Eisenstein integers. Therefore there exist countably many Eisenstein integers (as there are obviously an infinite amount of them). On the other hand there are uncountably many directions that you can look in so therefore the number of directions you can look in is infinitely larger than the number of Eisenstein integers.

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