Limit Of Sum Divided By Natural Logarithm

Calculus Level 4

lim m 1 ln ( m ) n = 2 m 1 n 1 + 1 ln ( n ) = ? \large\lim_{m\to\infty} \dfrac{1}{\ln(m)} \sum_{n=2}^{m} \dfrac{1}{n^{1 + \frac{1}{\ln(n)}}}=\ ?

e e 1 e \dfrac{1}{e} 1 1 1 2 \dfrac{1}{2}

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1 solution

Chew-Seong Cheong
Mar 21, 2018

Relevant wiki: Harmonic Number

L = lim m 1 ln m n = 2 m 1 n 1 + 1 ln n = lim m 1 ln m n = 2 m 1 e ln n + 1 = lim m 1 ln m n = 2 m 1 e n = lim m H m 1 e ln m where H m = n = 1 n 1 n , the n th harmonic number. = lim m ln m + γ 1 e ln m where γ is the Euler-Mascheroni constant. = 1 e \large \begin{aligned} L & = \lim_{m \to \infty} \frac 1{\ln m}\sum_{n=2}^m \frac 1{n^{1+\frac 1{\ln n}}} \\ & = \lim_{m \to \infty} \frac 1{\ln m}\sum_{n=2}^m \frac 1{e^{\ln n+1}} \\ & = \lim_{m \to \infty} \frac 1{\ln m}\sum_{n=2}^m \frac 1{en} \\ & = \lim_{m \to \infty} \frac {{\color{#3D99F6}H_m} - 1}{e\ln m} & \small \color{#3D99F6} \text{where }H_m = \sum_{n=1}^n \frac 1n \text{, the }n\text{th harmonic number.} \\ & = \lim_{m \to \infty} \frac {{\color{#3D99F6}\ln m + \gamma} - 1}{e\ln m} & \small \color{#3D99F6} \text{where }\gamma \text{ is the Euler-Mascheroni constant.} \\ & = \boxed{\dfrac 1e} \end{aligned}

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