Professor Cardy

Prime Number Calculator

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


80491 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: `80491` is 1 more than `80490` (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 `80491` is `6478801081`. Subtracting 1, we get `6478801080`. Note that `6478801080 ÷ 24 = 269950045`.

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: `80491 = 40246^2 - 40245^2 = 1619740516 - 1619660025`

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: `80491` is of the form `4n-1`, where `n = 20123`.

The First 10,000 Prime Numbers