TITLE: Is $\arcsin(1/4) / \pi$ irrational?
QUESTION [6 upvotes]: Is $\arcsin(1/4) / \pi$ rational? An approximation given by a calculator seem to suggest that it isn't, but I found no proof. Thanks in advance!

REPLY [14 votes]: This is a partial case of the classical result.
https://en.wikipedia.org/wiki/Niven%27s_theorem