Quantum chain is studied in one dimension.  The spectrum of the Hamiltonian was found by Hans Bethe in 1931.  I study the probability of formation of ferromagnetic string in the antiferromagnetic ground state, which is called emptiness formation probability P(n).  This is the most fundamental correlation function.  It is proven that for the small n, P(n) can be expressed in terms of the Riemann zeta function with odd arguments, logarithm ln 2 and rational coefficients.  This adds yet another link between statistical mechanics and number theory.  The asymptotic of P(n) is also studied.