Power Serieshard
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Consider the product of two series f(x)=n=0xnf(x) = \sum_{n=0}^{\infty} x^n and g(x)=n=0xnn!g(x) = \sum_{n=0}^{\infty} \frac{x^n}{n!}. What is the coefficient of x2x^2 in their Cauchy product (fg)(x)(f \cdot g)(x)?