<p>I am an ex-mathematician who still enjoys solving math problems. Here is a selection of my answers:</p>
<p><a href="https://math.stackexchange.com/q/4355562/9340">Showing <span class="math-container">$\frac{3\sqrt{3}}{2\pi}\sum_{z\in\Lambda}\frac1{1-\left(\frac{z}{\sqrt3}-1\right)^3}=1$</span>, with <span class="math-container">$\Lambda$</span> a lattice</a></p>
<p><a href="https://math.stackexchange.com/q/3329646/9340">Limiting distribution of <span class="math-container">$\frac{1}{n} \sum_{k=1}^{n}|S_{k-1}|(X_k^2 - 1)$</span>, where <span class="math-container">$X_k$</span> are i.i.d. standard normal</a></p>
<p><a href="https://math.stackexchange.com/q/1965012/9340">Does the sum <span class="math-container">$\sum_{n \geq 1} \frac{2^n\text{ mod } n}{n^2}$</span> converge?</a></p>
<p><a href="https://math.stackexchange.com/q/2209895/9340">Expected absolute difference between two i.i.d. variables</a></p>
<p><a href="https://math.stackexchange.com/q/3102881/9340">Does the sequence <span class="math-container">$x_{n+1} = -16 + 6x_n + \frac{12}{x_n}$</span> converge?</a></p>
<p><a href="https://math.stackexchange.com/q/2866642/9340">Proving <span class="math-container">$\lim_{x \to 0+} \sum_{n=0}^\infty (-1)^n/(n!)^x = \frac{1}{2}$</span></a></p>
<p><a href="https://math.stackexchange.com/q/2619818/9340">Solution of the functional equation <span class="math-container">$f(x) + f(y) = f(x + y + 2f(xy))$</span></a></p>
<p><a href="https://math.stackexchange.com/q/2391594/9340">How to prove the existence of this limit?</a></p>

Sangchul Lee