Answer to the home page question:  (5π/3)(3√2 − 4)

See Weisstein, Eric W. “Sphere-Sphere Intersection.” From MathWorld—A Wolfram Web Resource. Link.

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Interesting complex valued function

The function $f(z) = \sum_{n=1}^{\infty} \left(\frac{z}{n}\right)^n$ is entire (holomorphic everywhere in the Complex plane). Its behaviour on and near the imaginary axis produces striking spiral patterns.

Project Euler