Eighteen is the cardinal number that follows seventeen and precedes nineteen. It is written as '18' in numerals and is a composite number composed of two digits, 1 and 8. In words, it is pronounced as 'eighteen' or 'one-eight'. In Roman numerals, it is written as XVIII. Eighteen is also a square number, being the sum of the first four odd numbers. It is also the sum of the first three cube numbers.