Characterizations of the Extended Geometric, Harris, Negative Binomial   and Gamma Distributions
  Extended geometric distribution is defined and its mixture is characterized by the property of having completely monotone probability sequence. Also, convolution equations and probability generating functions are used to characterize extended geometric distributions. Further, some characterizations of Harris and negative binomial distributions based on probability generating functions are obtained. Relations between these distributions are derived and finally a gamma distribution is characterized in terms of its Laplace transform. 
E Sandhya, S Sherly, M K Jos and N Raju