Tool to find the closest prime number of a number, the prime number nearest to a given number also called closest Prime function

Closest Prime Number - dCode

Tag(s) : Arithmetics

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No mathematic formula can find the **nearest prime** number of another given number. dCode uses algorithms based on probabilistic primality tests for numbers greater or lower than the number requested, and then checks it via deterministic algorithms.

__Example:__ The **closest prime** number to `100` is `101`

__Example:__ The **nearest prime** number to `1000` is `997` (the next is `1009`)

__Example:__ The **closest prime** number to `10000` is `10007`

If the next prime number and the previous prime number are at the same distance, dCode returns the next prime number.

Two prime numbers are called twins if their difference is 2 (the **nearest prime** number is at a distance of 2 units).

__Example:__ 5 and 7 are twins because 7-5 = 2.

The OEIS lists 2 series of numbers:

A051697: 2, 2, 2, 3, 3, 5, 5, 7, 7, 7, 11, 11, 11, 13, ... which for any integer N associates its **nearest prime** number (the smallest in the case of a tie)

A077018: 2, 2, 2, 3, 5, 5, 7, 7, 7, 11, 11, 11, 13, 13, ... which for any integer N associates its **nearest prime** number (the largest in case of a tie)

The 2 sequences are identical except for the number `3` which appears twice in the first sequence but only once in the second one.

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Source : https://www.dcode.fr/closest-prime-number

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