Professor Cardy

Prime Number Calculator

PORTUGUESE ENGLISH SPANISH FRENCH GERMAN CHINESE

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


71 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: `71` is 1 less than `72` (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 `71` is `5041`. Subtracting 1, we get `5040`. Note that `5040 ÷ 24 = 210`.

3) Difference of squares: Every prime number greater than 2 can be expressed as the difference of the squares of two positive integers.
Example: `71 = 36^2 - 35^2 = 1296 - 1225`

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: `71` is of the form `4n-1`, where `n = 18`.

The First 1000 Prime Numbers