ke for k = 0, 1, 2, . . . . (2.15) Again, this gives rise to

λke−λ for k = 0, 1, 2, . . . . (2.15)

Again, this gives rise to a mass function since

∞X k=0 1

k!

λke−λ = e−λ ∞X k=0 1

k!

λk = e−λeλ = 1.