Professor Cardy

Prime Number Calculator

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Enter an integer (max. 1,000,000)


2557 is a prime number.

About the Calculator

This calculator performs the decomposition of a number into its prime factors and lists all its natural divisors. Enter an integer between 1 and 1,000,000.

Curiosities

1) Relation to multiples of 6: Every prime number greater than 3 is always one less or one more than a multiple of 6.
Example: `2557` is 1 more than `2556` (multiple of 6).

2) Square minus 1 divisible by 24: For every prime number greater than 3, if 1 is subtracted from its square, the result is always divisible by 24.
Example: The square of `2557` is `6538249`. Subtracting 1, we get `6538248`. Note that `6538248 ÷ 24 = 272427`.

3) Difference of squares: Every prime number greater than 2 can be expressed as the difference of the squares of two positive integers.
Example: `2557 = 1279^2 - 1278^2 = 1635841 - 1633284`

4) Sum of two squares: Every prime number of the form `4n+1` (where n is a positive natural number) can be expressed as the sum of two squares.
Example: `2557 = 21^2 + 46^2 = 441 + 2116`, where `2557 = 4 × 639 + 1`.

5) Form `4n+1` or `4n-1`: Except for the number 2, all prime numbers follow the pattern `4n+1` or `4n-1`, where `n` is a natural number.
Example: `2557` is of the form `4n+1`, where `n = 639`.

The First 1000 Prime Numbers