You Win the Internet’s Dumbest Person Award!
Hm… We never really thought about this. Four is the only number with the same number of letters in it as its value. Five has four letters, six has three, seven has five, eight has five, and so on. Ah, but do you see where the OP made a mistake?
One helpful commenter pointed out that, in fact, four was not the only number with the same number of letters as its numerical value. Did the OP completely forget about the number to? Yes, they did. Thank you, commenter, for murdering a clump of our brain cells with your answer.