647 is the sum of the five prime numbers from 113 to 139.

647 appears in only one Pythagorean triple, the primitive 647-209304-209305.

Print the puzzles or type the solution on this excel file: 10 Factors 2015-10-12

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- 647 is a prime number.
- Prime factorization: 647 is prime.
- The exponent of prime number 647 is 1. Adding 1 to that exponent we get (1 + 1) = 2. Therefore 647 has exactly 2 factors.
- Factors of 647: 1, 647
- Factor pairs: 647 = 1 x 647
- 647 has no square factors that allow its square root to be simplified. √647 ≈ 25.43619.

**How do we know that ****647**** is a prime number?** If 647 were not a prime number, then it would be divisible by at least one prime number less than or equal to √647 ≈ 25.4. Since 647 cannot be divided evenly by 2, 3, 5, 7, 11, 13, 17, 19, or 23, we know that 647 is a prime number.

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