Sorting a single number

What is the only number that, when written in English, gives a sequence of letters which is sorted alphabetically?

(The original phrasing of the question was meant to be a bit less straightforward to answer, as one had to come up with a way in which a single number can be 'sorted', but you didn't like it...)

• written down on its own? Couldn't understand this – L.K. Apr 6 '17 at 13:35
• What does it mean to sort a number? Is this computer science jargon? – GoldenGremlin Apr 6 '17 at 13:37
• This sounds rather broad. I could easily say that 10, 12,13,14,15,16,17,18,19, etc are sorted by their digits... – dcfyj Apr 6 '17 at 13:41
• @L.K.: written down on its own might refer to placing the number above itself. Like how 8 can be created with 2 0's, although that might be a bit far fetched. – Stefan Apr 6 '17 at 14:43
• @Silenus Obviously sorting refers to seeing which postcode/ZIP code it belongs to, then seeing whether the corresponding locality is alphabetical (contains only letters). :P – boboquack Apr 8 '17 at 8:37

I guess that the answer you are looking for is ...

... forty.

It is the only number whose letters are sorted alphabetically when written in English.

Consider

ONE,

whose letters are sorted in reverse alphabetical order when written in English.

There are more possibilities:

• trivial:

$e$, $i$

• in a reverse alphabetical order:

$\pi$ (= pi when written down in English), 0 (if written down as oh)