# Questions tagged [factorial]

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7 questions
1answer
411 views

### Asymptotics question

Is $\frac {n!} {2!\cdot 4!\cdot 8!\dots (n/2)!}=O(4^n)$? I am really stuck and I tend to believe it's true, but I don't know how to prove it. Any help would be appreciated!
0answers
25 views

### Where f(n) = n! belongs to? P, co-P, NPComplete or NPHard? [duplicate]

Where f(n) = n! belongs to? P, co-P, NPComplete or NPHard?
1answer
404 views

### Why is the complexity of factorial a function of n?

When we compute the complexity of calculating factorial of a number $n$ why is it in terms of $n$ instead of the number of the number of bits occupied by the number of bits occupied by $n$ (like we do ...
0answers
429 views

### Can factorial be done in O(1) and proof?

The typical way to compute the factorial would take $O(n)$ because it calls itself recursively. However, there are many other ways to compute the factorial function based off the gamma function, ...
1answer
171 views

### Complexity calculation using a recurrence relation [duplicate]

I just can't solve this problem, I'm new to reccurences. I have this recurrence $T(n)=n*T(n-1)$ $T(1)=1$ The second term will be: $T(n-1)=(n-1)*T(n-2)$ And so on. It's complexity is O(n!) but i ...
0answers
296 views

### How to get from factorial to a y-combinator?

In one of his conference talks Jim Weirich derives the applicative form of the y-combinator by refactoring a partial definition of factorial. The starting point in his talk is different than what ...
1answer
79 views

### Generating all factorials up to $n$: faster than naive approach?

I'm aware of prime decomposition and parallel approaches to calculating one factorial; however, if I want the factorials of all numbers up to $n$, is there anything more efficient than the naive ...