  We compute the topological susceptibility of the SU(N) Yang-Mills theory in
the large-N limit with a percent level accuracy. This is achieved by measuring
the gradient-flow definition of the susceptibility at three values of the
lattice spacing for N=3,4,5,6. Thanks to this coverage of parameter space, we
can extrapolate the results to the large-N and continuum limits with
confidence. Open boundary conditions are instrumental to make simulations
feasible on the finer lattices at the larger N.
