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5 votes

Non-commutativity of the d'alambert operator acting on the covariant derivative of a scalar ...

Use $$ [\nabla_\mu,\nabla_\nu]V^\rho=R_{\mu\nu}{}^{\rho\sigma} V_\sigma $$ to conclude that $$ \begin{aligned} {}[\nabla^\nu\nabla_\nu,\nabla_\mu]\phi&\overset{ \mathrm A}=\nabla^\nu[\nabla_\nu,\nabla …
AccidentalFourierTransform's user avatar
8 votes

Does this multiplicative function have a name? If so, what is known about it?

This is also called the Dedekind $\psi$ function: $$ \psi(n):=n\prod_{p|n}(1+p^{-1}) $$ See also A001615 and A158523.
AccidentalFourierTransform's user avatar
10 votes

A special type of generating function for Fibonacci

Perhaps interesting to note the following. In the notation of Henri Cohen, $$ F(x)=1 + x+\frac{x^2}{\color{red} 2}-\frac{x^3}{\color{red} 3}+\frac{x^4}{\color{red}8}+\frac{x^5}{15}-\frac{25 x^6}{\col …
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