What is the least number of presidential electors a state may have?

Three. Every state has exactly 2 senators in the U.S. Senate, while the number of representatives in the U.S. House vary from state to state. A state by law, though must have at least one congressman. Since number of electors is based on total number of senators and congressmen of a state, 2 senators + 1 congressman= 3 total electors minimum.