In what concerns the continuous evaluation solving exercises grade during the semester, you should submit until 23:59 of November 2nd
(this exercise will still be available for submission after that deadline, but without counting towards your grade)
[to understand the context of this problem, you should read the class #04 exercise sheet]

In this problem you should submit a function as described. Inside the function do not print anything that was not asked!

[IP031] Combinatorial Calculations

In mathematics, a combination is a selection of items from a set that has distinct members, such that the order of selection does not matter. If the set has n elements, the number of combinations of size k is denoted by \( C_{n,k} \) and can be computed as follows: \[ C_{n,k} = \frac{n!}{k!(n - k)!} \] Can you help calculate the number of combinations?

The Problem

Write a function combination(n, k) that, given two integers n and k, returns \( C_{n,k} \). Note that if \(k > n \), then \( C_{n,k} \) should return the string "NA" (Not Applicable).

Constraints

The following limits are guaranteed in all the test cases that will be given to your program:

print(combination(6, 2))
print(combination(15, 9))
print(combination(100, 4))
print(combination(3, 9))

15
5005
3921225
NA