Unexpected appearances of $\pi^2 /~6$.
61794
Interesting and unexpected applications of $\pi$
151000
Area of a weird ellipse shape.
148940
$\sum_{n=1}^\infty\frac1{n^6}=\frac{\pi^6}{945}$ by Fourier series of $x^2$
22842
The Interpretation of $|\psi|^2$ and the No-Clone Theorem
126040
Geometric explanation of $\sqrt 2 + \sqrt 3 \approx \pi$
148576
Origin of rapidly converging sequence for $e^\pi$
40837
Why $e^{i(π/3)} \ne -1$?
130078
How can one prove that $\pi^4 + \pi^5 < e^6$?
68824
Show that $\frac{(3^{77}-1)}{2}$ is odd and composite
21152
Exactly half of the elements of $\mathcal{P}(A)$ are odd-sized
154900
Why is $\pi$ = 3.14... instead of 6.28...?
105177
Gosper's unusual formula connecting $e$ and $\pi$
136736
Is there a $(6,9,3)_2$ code?
116283
How to properly interpret a seemingly contradictory result in Mathematica?
104548
Geometric proof for irrationality of $\pi$
128098
Decimal Expansion of Pi
52517
Construction of $\mathbb{CP}^2$ from $S^2\times S^2$