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Is 18 a prime number?

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Is 18 a prime or composite number?

Answer

Number 18 is not a Prime

18 = 2 × 3²

18 has 6 divisors — 1, 2, 3, 6, 9 and 18; a prime has exactly two: 1 and itself.

Primes up to √18

4² = 16 ≤ 18 < 25 = 5², so it is enough to try primes up to 4

÷2 divides

18 ÷ 2 = 9 — 2 divides 18, so 18 is composite

Nearest primes: 17 and 19

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See Also

Factors of a Number - List all Factors and Factor Pairs of a Number
Prime Factorization - Prime Factorization Calculator
Prime Numbers List - List of all Prime Numbers - how many Prime numbers are between

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Is 18 a prime number? Is 18 a prime number? 18 is a composite number. Check if any number is prime or composite with our free online prime checker.

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Prime numbers list

Number	Is Prime
3	Yes
4	No: 2²
5	Yes
6	No: 2 × 3
7	Yes
8	No: 2³
9	No: 3²
10	No: 2 × 5
11	Yes
12	No: 2² × 3
13	Yes
14	No: 2 × 7
15	No: 3 × 5
16	No: 2⁴
17	Yes
18	No: 2 × 3²
19	Yes
20	No: 2² × 5
21	No: 3 × 7
22	No: 2 × 11
23	Yes
24	No: 2³ × 3
25	No: 5²
26	No: 2 × 13
27	No: 3³
28	No: 2² × 7
29	Yes
30	No: 2 × 3 × 5
31	Yes
32	No: 2⁵

FAQ

Is 18 a prime or composite number?

Number 18 is not a Prime

How many factors are in a number 18?

6

How to check if 18 is prime?

Divide 18 by the primes in order: 4² = 16 ≤ 18 < 25 = 5², so it is enough to try primes up to 4. The first one that divides it is 2: 18 ÷ 2 = 9, so 18 is composite.