I figured out that this is Poisson distribution with a parameter λ >0
P(X = k) = ((λ^k)/k!)e^−λ , k = 0, 1, . . . ,
And now I want to show that the values of this distribution sum up to 1. Any help is appreciated. Thank you

I figured out that this is Poisson distribution with a parameter λ >0
P(X = k) = ((λ^k)/k!)e^−λ , k = 0, 1, . . . ,
And now I want to show that the values of this distribution sum up to 1. Any help is appreciated. Thank you