How can $0!=1$ if the definition of factorial is $n!=n\times (n-1)!$
2959
Prove $0! = 1$ from first principles
75123
If $p$ be a prime and r be any integer, $0 < r < p$ then $\frac{(p-1)!}{r!(p-r)!}$ is an integer.
136077
Prove that $x-1$ is a factor of $x^n-1$
61117
Prove by induction: $n! \ge 2^{(n-1)}$ for any $n \ge 1$
62177
Prove that: $2^n < n!$ Using Induction
100558
Prove that for any even positive integer $n$, $n^2-1 \mid 2^{n!}-1$
158335
Why is this $0 = 1$ proof wrong?
89413
Can there be only one extension to the factorial?
132732
Estimate of n factorial: $n^{\frac{n}{2}} \le n! \le \left(\frac{n+1}{2}\right)^{n}$
86413
Show that $\frac{(m+n-1)!}{m!n!}$ is an integer where m and n are positive integers and gcd(m,n)=1
141088
Proof : $2^{n-1}\mid n!$ if and only if $n$ is a power of $2$.
1507
The product of $n$ consecutive integers is divisible by $n$ factorial
34299
Combinatorial proof of $\sum_{k=0}^n k \cdot k! = (n+1)! -1$
7894
Does it follow that $(n!)^n$ divide $(n^2)!$
56474
An example where $\frac{(2m)!(2n)!}{m!n!(m + n)!}$ is the number of ways of counting something?
97534
Ruby factorial function
61673
Could I define 0^0 to be 1?