Prime Numbers Math Example 3

Follow the full solution, then compare it with the other examples linked below.

Example 3

easy
List all prime numbers between 20 and 40.

Solution

  1. 1
    Check each number: 21 = 3×73 \times 7, 22 = 2×112 \times 11, 23 is prime, 24–28 are composite, 29 is prime, 30–30 composite, 31 is prime, 32–36 composite, 37 is prime, 38–40 composite.
  2. 2
    The primes are: 23,29,31,3723, 29, 31, 37.

Answer

23,29,31,3723, 29, 31, 37
Systematically test each candidate by checking divisibility by small primes. Memorizing small primes helps speed up factorization problems.

About Prime Numbers

Integers greater than 1 whose only positive divisors are 1 and themselves—they cannot be factored further.

Learn more about Prime Numbers →

More Prime Numbers Examples

Example 1 easy

Find the prime factorization of [formula].

Example 2 medium

Determine whether [formula] is prime.

Example 4 easy

Is [formula] prime or composite?

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