Cliff Pickover poses a math challenge: can anyone determine the sign of sin(99^9999!)?
pickover · x · 2026-10-25
Science writer Cliff Pickover shares a playful math challenge: a mathematician emerges from a cave and hands you a slip of paper reading sin(99^9999!), asking whether today's technology or brainpower can even determine if the value is positive or negative.
The number is far too large to compute directly — the trick lies in modular arithmetic and the periodicity of sine to reason about which quadrant the angle lands in. Such puzzles are popular tests of mathematical reasoning and are often used to probe the limits of AI models' reasoning ability.
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