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Tool to search for prime numbers located before a number, or the nth previous prime number smaller than/inferior to a given number.

Answers to Questions

How to calculate the previous prime number?

No mathematical formula allow to automatically calculate the prime number preceding any number N (less than N). dCode performs primality tests on numbers below the requested number until a prime number is found.

Example: The largest prime number that precedes 100 is 97

Example: The 10th prime number preceding 1000 is 937 (so there is a list of 9 prime numbers between 938 and 999 included)

The number N must be a positive real number.

How to find greatest primes with n digits ?

The first prime number before $ 10^n $ is a number with $ n $ digits which is the greast n-digit coprime number.

Example: 7, 97, 997, 9973, 99991, etc.

What are twin primes numbers?

A prime number and the previous prime number are twins primes when their difference equals 2.

Example: 11 and 13 are called twins primes as 13-11 = 2.

Source code

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