The compound negative binomial distribution with exponential claim amounts
(severity) d~stribution is shown to be eqmvalent to a compound binomial
distribution with exponential claim amounts (severity) with a different
parameter. As a result of this, the distribution function and net stop-loss
premmms for the Negative Binomial-Exponential model can be calculated
exactly as finite sums if the negative binomial parameter a is a positive integer.
The result is a generalization of LUNDBERG 0940).