In Prime Obsession: Bernard Riemann and the Greatest Unsolved Problem in Mathematics, author John Derbyshire tells a fabulous story about arguably the greatest mathematician that ever lived, Carl Friedrich Gauss. Gauss was one of, if not the first mathematician to shine light on the Prime Number Theorem which led to the now infamous Riemann Hypothesis. In any event, when Gauss (1777-1855) was 10 years old (as the story goes), his schoolmaster decided that he needed an hour or so break from the classroom so he assigned the following problem to the kids: add up every numeral between 1 and 100. Almost instantly, before the master had even sat back down at his desk, Gauss threw his slate onto the master’s desk, exclaiming “ligget se!” or ‘there it is!’
Gauss had mentally listed the numbers 1-100 horizontally across, did the same in reverse order, and summed the two rows vertically so that each column totaled 101. So Gauss knew that there were 100 occurrences of 101, but since each number was listed twice, Gauss had to halve the sum to get the final answer: 50 x 101 or 5,050. It’s so simple, elegant, and brilliant it’s dumbfounding.