Professor Cardy

Prime Number Calculator

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


24781 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: `24781` is 1 more than `24780` (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 `24781` is `614097961`. Subtracting 1, we get `614097960`. Note that `614097960 ÷ 24 = 25587415`.

3) Difference of squares: Every prime number greater than 2 can be expressed as the difference of the squares of two consecutive natural numbers.
Example: `24781 = 12391^2 - 12390^2 = 153536881 - 153512100`

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: `24781 = 70^2 + 141^2 = 4900 + 19881`, where `24781 = 4 × 6195 + 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: `24781` is of the form `4n+1`, where `n = 6195`.

The First 10,000 Prime Numbers