Definition:Exponential Generating Function

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Let $A = \sequence {a_n}$ be a sequence in $\R$.

Then $\ds \map {G_A} z = \sum_{n \mathop \ge 0} \frac {a_n} {n!} z^n$ is called the (exponential) generating function for the sequence $A$.

The mapping $\map {G_A} z$ is defined for all $z$ for which the power series $\ds \sum_{n \mathop \ge 0} \frac {a_n} {n!} z^n$ is convergent.

The definition can be modified so that the lower limit of the summation is $b$ where $b > 0$ by assigning $a_k = 0$ where $0 \le k < b$.

Also see