Er. alokpandey's Blog

A regular expression to check for prime numbers

Posted in Uncategorized by Alok Kumar Pandey on July 31, 2010

Regular expressions are extremely powerful. This is something I read at least once or twice every day while reading articles and blogs on the Web.

While browsing today, I found this page which thoroughly describes the use of the regular expression /^1?$|^(11+?)\1+$/ in Perl to check if a number is prime or not!!!

To be frank, I was skeptical. The regular expression looks like magic! And I wanted to understand it better. I rewrote it in Ruby using irb and I tested it:

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