Of all the numbers whose literal representations in capital letters consists only of straight line segments (for example, FIVE), only one number has a value equal to the number of segments used to write it. Which number has this property?

Why this works

This riddle plays with both the visual representation of numbers and the concept of counting the straight line segments in their capital letter forms. When you write "TWENTY NINE" in capital letters, you can break it down as follows: T (2), W (4), E (4), N (2), T (2), Y (3), space (0), N (2), I (2), N (2), E (4). Adding these segments together gives you 2 + 4 + 4 + 2 + 2 + 3 + 0 + 2 + 2 + 2 + 4 = 29, which matches the numerical value of the phrase "TWENTY NINE." Thus, it’s the only number that equals the total number of straight line segments used to write it!