Probability Mass Function

Is the function f(x) = c(x+1)^2 for X = 0, 1, 2, 3, a probability mass function? Explain

why or why not. I am not exactly sure how you can tell if something is a pmf? I looked in my textbook but it doesn't really explain it so I can understand it. Thanks to anyone who can help.

Re: Probability Mass Function

It really depends on what 'c' is.

Do you mean you need to find 'c' s.t f(x) is a pmf?

Re: Probability Mass Function

I am not entirely sure. The problem doesn't say what 'c' is. I was thinking that it was just a constant. Can you determine if the problem is a pmf if you assume 'c' to be a constant?

Re: Probability Mass Function

If X=0,1,2,3 only, then $\displaystyle \displaystyle \sum_{i=0}^3f(i)= 1$