Congruence classes

Congruence classes are a way to group numbers based on a specific relationship called "congruence." When two numbers have the same remainder when divided by a particular number (called the modulus), they belong to the same class. For example, under division by 3, the numbers 2, 5, and 8 are in the same class because each leaves a remainder of 2 when divided by 3. These classes help organize numbers into categories that behave similarly under certain arithmetic operations, making them useful in modular arithmetic, cryptography, and number theory.