The simple counts. I can make Mathematica do them (using CS notation, P(n,r) and C(n,r)). Is there a reason that these don't exist as simple built-in functions (or can I just not find them)?
In[112]:= Pochhammer[3, 2] Out[112]= 12
But 3P2 = 6, not 12
Thanks, Daniel, I hadn't thought to do that.
But for my own convenience, I will create a user-defined function as suggested by Gianluca.
That doesn't answer the original question, which is one I have as well. Why aren't these native to Mathematica?
Binomial (which counts combinations) and Pochhammer (which counts permutations) are both Mathematica system functions.
Binomial
Pochhammer
You might also take a look at Pochhammer and FactorialPower.
FactorialPower
Binomial makes sense. That's what I figured for Perm. Thanks.
The function C is called Binomial in Mathematica. The function P does not appear to be pre-installed, but you can define it yourself:
C
P
P[n_, r_] := n!/(n - r)!
