Fundamental theorem of arithmetic

Every whole number is a unique product of primes — no exceptions.

Every whole number greater than 1 is either prime, or can be written as a product of primes — uniquely (up to order).

Try it

Factor 60

60 = 2 × 2 × 3 × 5. No other prime factorization is possible.

This is why primes are called the 'building blocks' of numbers.