Behold an ancient Japanese "Sangaku" table -- the Sudoku of the 17th century.

Sangaku emerged during the 100-year period that Japan forcibly cut itself off from West, allowing only one Dutch ship a year to dock. The cultural isolation did some weird things to the country's mathematicians. Because they never heard about calculus -- which was developed in Europe -- they developed brute-force ways of solving classic calculus problems, such as how many circles of a particular size fit in a square. They'd draw the enormous, sprawling solutions out on beautifully illustrated wooden tables, which they regarded as religious offerings. (I love it: Using math to praise God. Man, wouldn't it be nice if more religious conservatives in the US made that connection? It's quite a venerable once, too, since many historic mathematicians -- most particularly Newton -- regarded math as the language in which God spoke.)

Anyway, Sangaku fell into disrepute during the 20th century, but Tony Rothman, a Princeton Nobel nominee, is helping spearhead a movement to restore what he calls the sudoku of the 17th century. Like Sudoku, Sangaku was based in principles so simple that children could solve them, as Rothman says in this story:

"Some of the tablets feature solutions provided by 12-year-olds," he said. "But that doesn't mean they were easy. Today's high school geometry problems tend to require only five or six lines to solve, whereas the old problems often demand pages and pages of work. Sangaku were more like math Olympics problems, or the sort of thing your teacher might have put on the wall for extra credit."