https://byjus.com/questions/the-sum-s-of-first-n-natural-numbers-is-given-by-the-formula-sequals-2n-n1-if-sequals231-find-n/
https://byjus.com/questions/the-sum-s-of-first-n-natural-numbers-is-given-by-the-formula-sequals-2n-n1-if-sequals231-find-n/