The puzzle is easily solved when there are five ranks and five regiments, or seven ranks and seven regiments. But after searching in vain for a solution for the case of 36 officers, Euler concluded that “such an arrangement is impossible, though we can’t give a rigorous...See more

The story goes that one day somebody challenged him with a puzzle. Two bicyclists start at opposite ends of a road 20 miles long. Each cyclist travels toward the other at 10 miles per hour. When they begin, a fly sitting on the front wheel of one of the bikes takes off and races...See more

Around 1900 B.C., a student in the Sumerian city of Nippur, in what’s now Iraq, copied a multiplication table onto a clay tablet. Some 4,000 years later, that schoolwork survives, as do the student’s errors (10 times 45, for example, is definitely not 270). The work is a reminder...See more