# Why do the mathematicians stated $0!$ to be $1$? [duplicate]

My question is very simple, if just as we say $5! = 120, 4! = 24,$ how can we say that $0! = 1$? Why did the ancient mathematicians conventionally consider $0!$ to be $1$? Then there's coming lot of anomaly, because $1! = 0!$. It's really strange. Can anyone state the exact cause?
• As we know $n!=n\times (n-1)!$, Put n=1, you will get that $0!=1$ – Chiranjeev_Kumar Aug 16 '15 at 8:51