Top network posts

• 39 Bijection $f\colon\mathbb{N}\to\mathbb{N}$ with $f(0)=0$ and $|f(n)-f(n-1)|=n$
• 15 Maximal subgroups that force solvability.
• 14 Abstract proof that $\lvert H^2(G,A)\rvert$ counts group extensions.
• 11 How to compute $\sum_{k=1}^{\infty}{\frac{1}{k^2+2k}}$?
• 8 If $y^2-x^2\bigm|2^ky-1$ and $2^k-1\bigm|y-1$ then $y=2^k$ and $x=1$
• 7 If $p^k|n!$ then $p!^k|n!$
• 7 Fundamental group of punctured simply connected subset of $\mathbb{R}^2$
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