Nineteen is the number that comes after eighteen and before twenty. It's written as 19 in numerals. When you count by ones from one to twenty, nineteen is the second-to-last number you say.

Nineteen is interesting mathematically because it's a prime number, meaning it can only be divided evenly by itself and one. If you tried to split nineteen cookies equally among two, three, four, or any other number of friends, you'd always have leftovers.

The number appears in many contexts: there are nineteen years between someone who's twenty and someone who's one year old. A person who is nineteen years old is often in their first year of college. The 1800s are called the nineteenth century because they were the nineteenth hundred years after year one.

When counting by tens, nineteen sits in an awkward spot. You've passed ten but haven't quite reached twenty, the next clean multiple of ten. Nineteen often appears in prices, such as $19.99 instead of $20.00, because nineteen dollars can seem cheaper even though it's only one penny less.