Curve collapse for the isospin-2 pion scattering length from QCD with 3, 4, and 5 colors

I show comparisons of the pion - pion scattering length in the isospin - two channel from simulations of of QCD with $N_c=3$, 4 and 5 colors and $N_f=2$ flavors of degenerate mass fermions. The scattering length varies as $1\mathrm{/}{N}_c$, as expected from large $N_c$ counting arguments.