Everyone knows "four" is the only name for a number less than 10 that has as many letters as the number says.
However...
"Fifty" and "seventy" are names for numbers more than 10, that have as many letters as their most significant digit says. Therefore "fifty-four" and "seventy-four" can be said as having as many letters as the numbers read out digit by digit.
That's not all, though:
Two multiples of nine, "thirty-six" and "Forty-five" have the same property, but backwards. The first word has as many letters as the second digit and the other way around.
I noticed all of this when trying to count the letters in Cornershop's weird song "A brimful of asha". What is asha, by the way?