Two fun facts about the number two are that it is the only even prime number and its root is an irrational number. All numbers that can only be divided by themselves and by 1 are classified as prime.
This test for evenness can be applied in bases other than decimal. For example, hexadecimal numbers that can be divided by two are even in both the decimal base and their respective base. Checking whether the single digit's part of a number is divisible by two is enough to tell whether the entire number is divisible. This means all numbers that end in two, four, six, eight and zero are even in the decimal and hexadecimal systems.
Although one is often confused as the first prime integer number, two is actually both the smallest and the first prime number. This is because it is the first integer to satisfy the definition of prime and be divisible by both one and itself, while one is only divisible by itself. Because three is the next prime number, two and three are the only two consecutive prime numbers. Two is also the base of the simplest numeral system that can express all natural numbers concisely: the binary system, upon which digital logic and computing are based. Two is also the first prime in the Fibonacci series.