Professor Cardy

Prime Number Calculator

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


2777 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: `2777` is 1 less than `2778` (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 `2777` is `7711729`. Subtracting 1, we get `7711728`. Note that `7711728 ÷ 24 = 321322`.

3) Difference of squares: Every prime number greater than 2 can be expressed as the difference of the squares of two positive integers.
Example: `2777 = 1389^2 - 1388^2 = 1929321 - 1926544`

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: `2777 = 29^2 + 44^2 = 841 + 1936`, where `2777 = 4 × 694 + 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: `2777` is of the form `4n+1`, where `n = 694`.

The First 1000 Prime Numbers