Power series/R/Fourth power/Fifth coefficient/Exercise

Let

$\sum _{n=0}^{\infty }a_{n}x^{n}$

be an absolutely convergent power series. Determine the coefficients of the powers ${}x^{0},x^{1},x^{2},x^{3},x^{4},x^{5}$ in the fourth power

${}\sum _{n=0}^{\infty }c_{n}x^{n}={\left(\sum _{n=0}^{\infty }a_{n}x^{n}\right)}^{4}\,.$

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