The numbers on your toaster typically indicate the level of toasting or browning that you want for your bread or other items. They usually represent the duration of toasting, not the temperature. Higher numbers usually correspond to longer cooking times, resulting in darker and toastier slices.
The heating elements inside the toaster stay at a constant temperature, and the toasting process is controlled by how long the heating elements stay on during each toasting cycle. As you increase the number setting, the heating elements stay on for a longer time, which leads to more browning of the bread.
Keep in mind that different toasters may have varying temperature ranges and cooking times associated with each number setting, so it's a good idea to test a few slices of bread at different settings to find the one that gives you the desired level of toasting.