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MathNet 2025 — 50 problems — Part 01 Question 49

Math Olympiad Vault · MathNet 2025 — 50 problems — Part 01

Question 49

Define $\operatorname{sgn}(x)$ to be $1$ when $x$ is positive, $-1$ when $x$ is negative, and $0$ when $x$ is $0$. Compute
$$
\sum_{n = 1}^{\infty}\frac{\operatorname{sgn}(\sin(2^{n}))}{2^{n}}.
$$
(The arguments to $\sin$ are in radians.)