The Four Color Theorem was not proven until 1976 and required the use of a computer.
I’m pretty sure the thing about arabic numerals representing the number of angles in their characters is total B.S.
Test Your Wits on These Mathematical Puzzles
by WILLIAM J. HARRIS
There’s nothing like a puzzle to test one’s mental alertness, and those presented here by Mr. Harris are certainly corkers. He also gives you some simple tricks which, though they only take a few minutes to learn, will convince your friends that you are a mathematical wizard of the first water. (P. S.— Answers are in the back of the book!)