SeriesCoefficient

SeriesCoefficient[series,n] finds the coefficient of the nth-order term in a power series in the form generated by Series. 

SeriesCoefficient[f,{x,x0,n}] finds the coefficient of (x-x0)n in the expansion of f about the point x=x0.

SeriesCoefficient[f,{x,x0,nx},{y,y0,ny},…] finds a coefficient in a multivariate series. 

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