Definition: The term "digamma" is derived from Greek and refers to a specific function in mathematical analysis, particularly for complex numbers. Specifically, it is defined as: $$ \psi(z) = \sum_{n=0}^{\infty} \frac{z^n}{n!} $$ This function is often used in probability theory, especially in the study of random variables and the gamma distribution. In other words, digamma functions are a special case of the gamma function, which
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