Different combinations possible Problem

Given a value n, imagine a mountain landscape inscribed in a reference (0, 0) to (2n, 0).
There musn't be white spaces between slopes and also the mountain musn't descend below the x axis.
The problem to be solved is: given n (which defines the size of the landscape) and the number k of peaks
(k always less than or equal to n), how many combinations of mountains are possible with k peaks?

Input 

n who represents the width of the landscape and k which is the number of peaks.

Output

Just the number of combinations possible.

Example

Given n=3 and k=2 the answer is 3 combinations.

Just to give a visual example, they are the following:

   /\     /\      /\/\
/\/  \   /  \/\  /    \


are the 3 combinations possible using 6 (3*2) positions and 2 peaks.

Edit:
 - more examples -

n  k  result
2  1  1
4  1  1
4  3  6
5  2  10


Winning condition

Standard code-golf rules apply. The shortest submission in bytes wins.
Python, 40 bytes



f=lambda n,k:k&lt;2or~-n*n*f(n-1,k-1)/~-k/k


Try it online!

Uses the recurrence \$a_{n,1} = 1\$, \$a_{n,k} = \frac{n(n-1)}{k(k-1)}a_{n-1,k-1}\$.