This is ζ(3) with the Riemann zeta function, a constant whose value is calculated with the infinite sum 1/1^{3}+1/2^{3}+1/3^{3}+1/4^{3}+... This constant is named after Roger Apéry, who proved it to be irrational. It is not known whether it's a transcendental number or not. This constant arises in a number of mathematical and physical problems.

Unlike ζ(2) and ζ(4), ζ(3) is not known to have a compact elementary expression.

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