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arXiv · 2202.10653

Multiplicative functions commutable with binary quadratic forms $x^2 \pm xy + y^2$

Poo-Sung Park
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Abstract

If a multiplicative function $f$ is commutable with a quadratic form $x^2+xy+y^2$, i.e., \[ f(x^2+xy+y^2) = f(x)^2 + f(x)\,f(y) + f(y)^2, \] then $f$ is the identity function. In other hand, if $f$ is commutable with a quadratic form $x^2-xy+y^2$, then $f$ is one of three kinds of functions: the identity function, the constant function, and an indicator function for $\mathbb{N}\setminus p\mathbb{N}$ with a prime $p$.

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Poo-Sung Park. 2022-02-22. Multiplicative functions commutable with binary quadratic forms $x^2 \pm xy + y^2$. https://arxiv.org/abs/2202.10653

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