Professor Cardy

Prime Number Calculator

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


63421 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: `63421` is 1 more than `63420` (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 `63421` is `4022223241`. Subtracting 1, we get `4022223240`. Note that `4022223240 ÷ 24 = 167592635`.

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: `63421 = 31711^2 - 31710^2 = 1005587521 - 1005524100`

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: `63421 = 139^2 + 210^2 = 19321 + 44100`, where `63421 = 4 × 15855 + 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: `63421` is of the form `4n+1`, where `n = 15855`.

The First 10,000 Prime Numbers