Professor Cardy

Prime Number Calculator

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


25219 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: `25219` is 1 more than `25218` (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 `25219` is `635997961`. Subtracting 1, we get `635997960`. Note that `635997960 ÷ 24 = 26499915`.

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: `25219 = 12610^2 - 12609^2 = 159012100 - 158986881`

4) 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: `25219` is of the form `4n-1`, where `n = 6305`.

The First 10,000 Prime Numbers