What is the Least Composite Number?

The Least (Smallest) Composite Number is 4. To understand why, we need to clearly define what composite numbers are.

Question (Click to Flip)

Is 1 a composite number?

Answer

No. 1 is neither prime nor composite. A composite number must have more than 2 factors. Since 1 has only one factor (itself), it does not qualify as composite.

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Key Facts

The list of composite numbers begins: 4, 6, 8, 9, 10, 12, 14, 15, 16, 18, 20... Note that all even numbers (except 2) are composite. Odd composites are less common: 9, 15, 21, 25, 27...

Definition of Composite Numbers

A Composite Number is a positive integer greater than 1 that has at least one positive divisor other than 1 and itself — i.e., it can be divided evenly by some number other than 1 and the number itself.

In other words, a composite number has 3 or more factors.

Examples:

4 = 1 × 4 and 2 × 2 → factors: 1, 2, 4 → Composite ✓
6 = 1 × 6 and 2 × 3 → factors: 1, 2, 3, 6 → Composite ✓
2 = 1 × 2 only → Prime (not composite)
3 = 1 × 3 only → Prime (not composite)

Why 4 is the Least Composite Number

Checking small numbers:

1: Has only 1 factor (1 itself). It is neither prime nor composite.
2: Has exactly 2 factors (1 and 2). It is a prime number (the only even prime).
3: Has exactly 2 factors (1 and 3). It is a prime number.
4: Has 3 factors (1, 2, and 4). It is composite ✓

Since 4 is the first number with more than 2 factors, 4 is the least composite number.

Questions and Answers

Is 1 a composite number?+

No. 1 is neither prime nor composite. A composite number must have more than 2 factors. Since 1 has only one factor (itself), it does not qualify as composite.

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