Marcin Mazur. Problem 10944. The American Mathematical Monthly, 109(5):475, 2002. [doi]
@article{Mazur02, title = {Problem 10944}, author = {Marcin Mazur}, year = {2002}, url = {http://www.jstor.org/stable/2695653}, researchr = {https://researchr.org/publication/Mazur02}, cites = {0}, citedby = {0}, journal = {The American Mathematical Monthly}, volume = {109}, number = {5}, pages = {475}, }