# Calculating Primes – Part 1

Today I am going to talk about calculating primes.

Not the Transformer movie in which Optimus Prime has to help the humans save the world.
I am talking about prime numbers in which the number is only divisable by one and itself.

The Algorithm that I am going to introduce is a brute force method for calculating prime numbers. It is great for comparing the computing power of two machines by looking at overall execution times.

This routine consists in dividing n by each integer m which is greater than 1 and less than or equal to the square root of n. If the result of any of these divisions is an integer, then n is not a prime; otherwise, it is a prime.

Most of the Perl coding used standard, built-in functions.

One exception was the date calculation package (Date::Calc) that I down loaded from CPAN to calculate the total elapsed time of the program. There is a bug in the perl package installer from Active State. Afer commenting out the offending line in web.pm, I used the command line ‘ppm install Date::Calc’ to add the package.

I always like to create a high level program algorithm before starting any coding. I usually write it in psuedo code so that is program like in nature.

Calculating Primes Algorithm:

Calculating Primes Algorithm:

The table below has the PERL script used in the solution and various supporting / output files. I ran the program to calculate all the prime numbers less than or equal to 2.5 Million. The program executed in 87 seconds on a Dell i5 Laptop running Windows 7 – 32 bit operating system and found 183,072 prime numbers.

 prg-calc-primes-v1.pl Calculate Primes Program primes.cmd Primes Batch File primes.log Primes Log File primes.csv Primes Result File image DOS Output Screen