Bourbaki

Exercise 5, § 2

Functions of a Real Variable, VII, 328

Let xnx_n be the root of the equation Γ′(x)=0\Gamma'(x) = 0 in the interval ]−n,−n+1[]-n, -n+1[. Show that

xn=−n+1log⁡n+O(1(log⁡n)2) x_n = -n + \frac{1}{\log n} + O \left( \frac{1}{(\log n)^2} \right)
(use the complements' relation and formula (5) of VII, p. 316). Deduce that
Γ(xn)∼(−1)n2π n−n−1/2 en+1 log⁡n. \Gamma(x_n) \sim \frac{(-1)^n}{\sqrt{2\pi}} \ n^{-n-1/2} \ e^{n+1} \ \log n .

Solution

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Transcribed from the printed volume. Not translated.