Bull. Korean Math. Soc. 2023; 60(1): 75-81
Online first article July 28, 2022 Printed January 31, 2023
https://doi.org/10.4134/BKMS.b210915
Copyright © The Korean Mathematical Society.
Poo-Sung Park
Kyungnam University
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 $p$.
Keywords: Additive uniqueness, multiplicative function, functional equation, quadratic form
MSC numbers: Primary 11A25, 11E20
Supported by: This work was supported by Kyungnam University Foundation Grant, 2019.
2021; 58(3): 603-608
2009; 46(3): 499-510
-0001; 31(1): 131-138
2015; 52(6): 1759-1776
© 2022. The Korean Mathematical Society. Powered by INFOrang Co., Ltd