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The least common multiple (aka the Lowest Common Multiple or Smallest Common Multiple) of two numbers / integers a and b, usually denoted by LCM(a, b), is the smallest positive integer that is divisible by both a and b.

Example: Lcm (3, 5) = 15.

Please note that both numbers must be different from zero.

The LCM is familiar from grade-school arithmetic as the "lowest common denominator" (LCD) that must be determined before fractions can be added, subtracted or compared.

The LCM of more than two integers is also well-defined: it is the smallest positive integer that is divisible by each of them.

When adding, subtracting, or comparing vulgar fractions, it is useful to find the least common multiple of the denominators, often called the lowest common denominator, because each of the fractions can be expressed as a fraction with this denominator.