## 21st Day of Year: 21.01.20

References: Inder J. Taneja, 2020 In Numbers: Mathematical Style – Revised, Zenodo, December 31, 2019, pp. 1-37, http://doi.org/10.5281/zenodo.3596193. Inder J. Taneja, Multiple-Type Pythagorean Triples, https://inderjtaneja.com/2018/08/04/2499/ Inder J. Taneja, Single Digits Representations of Numbers from 1 to 20000 , https://inderjtaneja.com/2019/01/01/single-letter-representations-of-numbers-from-1-to-20000/