Excess Kurtosis of Pareto Distribution/Lemma 3

Lemma for Excess Kurtosis of Pareto Distribution

 * $6 a^2 \paren {a - 1}^2 \paren {a - 2} \paren {a - 3} \paren {a - 4} = 6 a^7 - 66 a^6 + 270 a^5 - 510 a^4 + 444 a^3 - 144 a^2$