© Steffen Weber, July 2001

__Prime numbers:__

A prime number N is a number that is evenly divisible only by itself and by the number one (e.g.: 2, 3, 5, 7, 11, 13, 17 ). The only even prime number is 2. All other primes are odd numbers.

__Twin primes:__

Primes that are consecutive odd numbers (e.g.: 3-5, 11-13, 41-43,179-181) are said to be twins, otherwise they are singles.

__Triangle numbers:__

A number N is a triangle number if we can arrange N objects into a triangular arrangement, as shown below.