Forty is the only number that, when spelled out, has its letters in alphabetical order. The word "first" also has its letters in alphabetical order, but "one" has them in reverse alphabetical order.
More numerical wordplay:
- Eighty-eight is the longest number that is typed strictly with alternating hands — if you ignore the hyphen.
- The word "interchangeability" can be used to form the most spelled-out numbers; you can rearrange it to write the numbers three, eight, nine, ten, thirteen, thirty, thirty-nine, eighty, eighty-nine, ninety and ninety-eight — if you add the hyphen.
- Four is the only number that, when spelled out, has the same number of letters as its meaning.