Daniel J. Velleman. Monthly Gems. The American Mathematical Monthly, 121(2):164, 2014. [doi]
@article{Velleman14, title = {Monthly Gems}, author = {Daniel J. Velleman}, year = {2014}, doi = {10.4169/amer.math.monthly.121.02.164}, url = {http://dx.doi.org/10.4169/amer.math.monthly.121.02.164}, researchr = {https://researchr.org/publication/Velleman14}, cites = {0}, citedby = {0}, journal = {The American Mathematical Monthly}, volume = {121}, number = {2}, pages = {164}, }