Let $Y_1, . . . , Y_n$ be a random sample from a zero-truncated Poisson distribution with probability mass function:
$p_Y (y|λ) = k\frac{λ^ye^{-y}}{y!},$
$k > 0, λ > 0, y = 1, 2, . . . ,$ where k is an unknown constant.
I know that the sum of a probability mass function is 1, but I do not know how to use this information to find $k$.