← Paradoxes & riddles
1:49
Why 0! Equals 1
the factorial of nothing
The factorial of a number, written with an exclamation mark, multiplies all the whole numbers down to 1: 3! is 3 times 2 times 1, which is 6. So what is 0!?
Source: A classic puzzle, retold by INFINITE SUM and fact-checked against our curated notes
Want another one?
Type the name of a paradox or riddle you've heard of, or browse the rest of the archive.