As Dave said Leo, the numbers are Briggs and Stratton numbers, not mower numbers so they are on the engine, not the mower frame. They are stamped on the black cowl (cooling air duct) that wraps around the top of the engine, with a hole in it where the air intake grill cover spins around. The numbers will be on the vertical surface on the left side of the cowl when viewed from where you stand to operate the mower. They will be in three groups, just like the example Dave gave you.
