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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 is used to automatically calculate the prime number preceding any number. dCode perform 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)

The number 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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