An ancient Chinese puzzle: find a number from its remainders under three divisions
There is a number of soldiers. Counted in rows of three, two are left over. Counted in rows of five, three are left over. Counted in rows of seven, two are left over. How many soldiers are there, at minimum?
Reveal the answer
23. The puzzle comes from the Sunzi Suanjing, a Chinese mathematics text from somewhere between the 3rd and 5th centuries AD, and it's the earliest known example of what's now called the Chinese Remainder Theorem, a method for reconstructing a number from its remainders under several different divisors, still used today in cryptography and computer error-correction.