Excess Kurtosis of Pareto Distribution/Lemma 1

Lemma for Excess Kurtosis of Pareto Distribution

 * $\paren {a - 1}^4 \paren {a - 2}^2 \paren {a - 3} = a^7 - 11 a^6 + 50 a^5 - 122 a^4 + 173 a^3 - 143 a^2 + 64 a - 12$