1, 11, 21, 1211, 111221. These are the first five elements of a number sequence. Can you figure out what comes next? If you're trying a bunch of arithmetic operations to make the numbers work, you're ...

Some of the most satisfying number puzzles require little mathematical know-how. In fact, cracking the one below calls for thinking that is quite nonmathematical. I don’t know where or when I first ...

From the second number onward, each number in the sequence is the product of the digits of its predecessor. The next two numbers are therefore 3 × 3 × 6 = 54 and 5 × 4 = 20. All subsequent numbers in ...