What is so unique about these numbers?

I had read part of this puzzle (can't recall where). I added another part to it. Of course if you have seen this before please let others take a crack at it.

Why are numbers 1 and 40 uniquely different than all other integers (numbers)?

The letters are in alphabetic (FORTY) or reverse-alphabetic (ONE) order.

• This site makes the same claim for 40. A mental check of 1~20 seems to support the claim for 1. This sounds good to me. Dec 27, 2017 at 18:09
• This is an impressive answer, but I think there is another integer with this property, namely 0. "Zero" is only one of its names. Another one, which can be found in commonly used dictionaries, is "oh".
– hvd
Dec 28, 2017 at 0:18
• @hvd oh is a contraction.
– Cœur
Dec 28, 2017 at 10:20
• @Cœur Citation needed. merriam-webster.com/dictionary/oh lists it as a complete word.
– hvd
Dec 28, 2017 at 10:24
• Oh is indeed a word. And people might use it when writing the speech of someone who says o for the digit 0. But dictionary citation, please, for "oh" meaning the integer zero. Dec 28, 2017 at 16:30

The last letter of these numbers can be removed and a word remains.

I could not think of any other numbers that satisfy this criteria. Hint: You only need to check the smaller numbers to see that no other numbers satisfy this condition.

• Interesting. +1 for unique thinking. Note Te is included in many dictionaries as a noun. Ten is the number of course
– DrD
Dec 27, 2017 at 13:24
• Thanks. Maybe I should have said valid Scrabble answers!
– user43622
Dec 27, 2017 at 13:30
• Si also in Dictionaries. My answer is different.
– DrD
Dec 27, 2017 at 13:32
• Si (if you take it be the symbol for Silicon) is a proper noun. But here: dictionary.com/browse/si "si is the syllable used for the seventh tone of a scale and sometimes for the tone B" That's a lower case "s". Uh oh.
– user43622
Dec 27, 2017 at 13:37
• 80 fits this as well.
– Bass
Dec 27, 2017 at 14:26