NEGBINOM.DIST function
    NEGBINOM.DIST(FailureCount, SuccessThreshold, Probability,
    IsCumulative) NEGBINOM.DIST(FailureCount; SuccessThreshold; Probability;
    IsCumulative)
  
  FailureCount
        Number or { Number }
      
      The number of failures in a set of trials.
SuccessThreshold
        Number or { Number }
      
      The threshold number of successes.
Probability
        Number or { Number }
      
      The probability of success in each trial.
IsCumulative
        Logical or { Logical }
      
      FALSE to calculate the probability density function and TRUE to calculate the cumulative distribution function.
Returns
        Number or { Number }
      
      A probability for a negative binomial distribution.
Returns a probability for a negative binomial distribution.
Example
      NEGBINOM.DIST(1, 1, 0.5,
      FALSE)NEGBINOM.DIST(1; 1;
      0,5; FALSE)
      
    
    Returns 0.25 (25%), the probability that heads will come up exactly once before tails has come up when tossing a coin.
  Partly derived from the OpenOffice.org documentation, licensed
  under the Apache License 2.0.