SOLVED 1. The problem statement, all variables and given/known data I am trying to prove that the poisson distribution is normalized, I think I've got an ok start but just having trouble with the next step. 2. Relevant equations A counting experiment where the probability of observing n events (0≤n<∞) is given by: P(n) = (μ^n)/n! * e^(-μ) Where μ is a real number. 3. The attempt at a solution Background (possibly incorrect) So it's discrete, as n will take integer values; I need a sum not an integral. Ʃ P(n) from n=0 to ∞ is just given by: Ʃ (μ^n)/n! * e^(-μ) And e^(-μ) does not vary with n, so: Ʃ P(n) = e^(-μ) * Ʃ (μ^n)/n! Important bit Now as I am trying to prove it is normalized, i need to get Ʃ P(n) = 1, so I assume my problem is getting from: (μ^n) / n! to e^μ Any tips or help would be much appreciated, thanks in advance.