Why do we have more than 200 consecutive nines?
With mu(n) the Möbius function, is the limit equal to $-2$?
Prove this identity [PF, 2000] relative to harmonic numbers whose indices are squares(!).
Ninth ACM-SIAM Symposium on Discrete Algorithms(SODA'98) (San Francisco, January 1998) based on the corresponding paper by Clément, Flajolet, and Vallée.