Pair the numbers: (1+100), (2+99)... fifty pairs of 101, so 1+2+...+100 = 5050. Lovely! But the schoolboy-Gauss tale is folklore - no 100, no 5050 in the first telling. The math is certain; the story, embroidered. Hold each accordingly.
Sources: americanscientist.org/article/gausss-day-of-reckoning
