Linked from
The 35 pages that link to Riemann zeta function, each with the reason it gives.
Analytic number theoryRelated: Its zeros and pole encode information about prime numbers.
Jacques HadamardRelated: Its zeros and pole encode the prime distribution that Hadamard studied.
Divisor functionRelated: The Dirichlet series of σₖ is ζ(s)ζ(s−k) in its region of convergence.
Möbius functionRelated: Its reciprocal Dirichlet series has the Möbius function as coefficients.
Stefan–Boltzmann constantRelated: Its value at four enters the integrated blackbody spectrum.