How much would a person that weighs 637 n on earth weigh on mars?

It's fairly easy to find a reference that lists the acceleration of gravity on each planetary

surface, so we don't have to slog through it ourselves with the planet's mass and radius.

On the surface of Mars, it's 3.7 m/s2 (compared to 9.8 on earth).

Weight = m g = (65) (3.7) = 240.5 newtons.