0, 1, 2, 4, 5, 6, 8, 10, 40, 46, 60, 61, 64, 80, 84.

These numbers all have something in common, but there's one missing from the set.

Which number is missing? (and preferably explain the logic too...)

42

It's the answer to life, the universe, and everything, yet isn't up there o.0 

Nope, it's not 42

Grr...

Is it in the beginning of the set?

In the middle?

At the end?

The set isn't really a sequence... these numbers just all share a common property.

There are 16 numbers with said property and I've given you 15 of them.

Okay, thanks.

Are they outputs from an equation, and we have to figure out the equation...?

Ooh, is the answer that they're all tangible numbers?

They're flexible?

Is it their differences that make them alike?

*no clue*

tangible numbers? 

So far I don't see anything relevant in your guesses 

Idk, maybe something like random numbers strewn across the countryside seemingly at random, like the Easter Island statues....?

Is this some sort of famous results from an experiment, or whatever?

...Or do I actually have to do math(s) to get it...?

The relationship is actually very non-mathematical.

Ohh...

Is it really that simpl then? I'm in such an over-anylitical mood today....

I'm too tired to not think...!

are they the winning numbers in the 2139 mega lottery draw......the missing number being 26?

Why 2139 Sir Montague? Is that form a movie or something?

Okay Super-King, do you have to have specific knowledge about something specific to figure this out, or can you figure this out by just using logic?

no, just a random number.....but he can't definitely say that it is wrong...

Well I see. Who knows. Maybe they will show up as the winning number in some kind of mega lottery in 2139.

gonna be a long wait to find out though....

They are not lottery numbers, nor do they correspond to any past event or anything like that.

They're linked by a property of the numbers themselves (though not a mathematical relationship)

do the number have to be converted into another format to see the answer?

do the number have to be converted into another format to see the answer?

You're thinking on the right lines, yes. 

Does the order matter?

Is the number between 10 and 40?  (that seems like the most logical place - it's the largest gap in this sequence)

When decoding this, do we need some other object to decode it? (like 4433555 555666 + cellphone keypad => hello)

The order is irrelevant.

The missing number is not between 10 and 40.

You don't need any reference object to decode it.

are these numbers counts of something?

is it 43?

Is this property a property of each of the individual numbers, or of the set as a whole?

is it a property of their decimal representation? (if we represented them in base 3, would it change things?)

is it a property of their english names? (zero, one, two, etc.)

DJ.. which cellphone kepad are you using? mines diffrent to that

1:symbols
2:abc
3:def
4:ghi
5:jkl
6:mno
7:pqrs
8:tuv
9:wxyz
0:shift entry mode, or something....

25? All the other numbers exept 2 & 5 are used more than ones!

Ah, but its not between 10 & 40, grrrrr

52

probably not it thou, but I have no clue

are these numbers counts of something? No

is it 43? No

Is this property a property of each of the individual numbers, or of the set as a whole? Each individual number has the same shared property

is it a property of their decimal representation? (if we represented them in base 3, would it change things?) No

is it a property of their english names? (zero, one, two, etc.) Yes

The answer is neither 25 nor 52.
 

I'm assuming that this property is easy to state - i.e. you could teach a 3-5 year-old how to get these numbers.
Is that right?

does it have anything to do with the letters in the words? (or is it a property of the words themselves?)

does it have anything to do with the letter 'e'?

You could explain the property to a kid pretty easily, yeah.

It is related to the letters in the words, and kind of a property of the words... but it's not just the words (there are no members of the set that aren't numbers)

Not related to the letter e any more than any other letter.

Wait, so:

There are only 16 of these numbers in the entirety of the English numeral system, you've displayed 15 of them above. The answer to the riddle is found by a relation in the letters of the numerals. All of these numbers share the property and it's not a sequence. No math is involved in deriving the answer.

Comment as needed on the above, pls?

Does it have something to do with 4?

The next number is 100

The numbers in that sequence all use up the rest of the vowels except a.

(In the course of this exercise, I've just realised that no number bet 0-99 uses a in its spelling!!)

But then whats to exclude any other number? Why 100?

100 is the first number to have a

Anything after that will have a too, so I just picked 100

no it doesn't

Oh?

One Hundred

no a's there

ARRRGHHH!

maybe 101 - one hundred and one

*pulling hair out*

You're right... I thought of that, and then got too excited

but then, using that logic, why doesn't the sequence go 0, 4, 5?

thats all you'd need, right?

It could be any sequence of numbers... I didn't think it mattered

Maybe we should keep thinking

SK, is that the complete list? (excluding the number we're missing)

Or could the sequence -and subsequent logic- continue after that?

There are only 16 of these numbers in the entirety of the English numeral system, Yes
you've displayed 15 of them above. Yes
The answer to the riddle is found by a relation in the letters of the numerals. Yes
All of these numbers share the property and it's not a sequence.Yes
No math is involved in deriving the answer. Yes

Does it have something to do with 4? No

The next number is not 100, and the relation is not about using up all the vowels.

The 16 numbers (the 15 given plus the answer to this riddle) are the entirety of the set of numbers satisfying the criteria.

100 is the first number to have a

the way i hear it, 1000 is the first number with an 'A' 

*was about to say that*

What about "one hundred and one"?

apparently its 'one hundred one'

Says you 

Anyway, first use of the letter A has nothing to do with the actual answer...

one hundred 'n one?

ah, but that 'n is an abbreviation of and.

Ipso facto, QED, I win... 

Well, let's see... It really depends on which language you use. The English Wikipedia accepts both "One
Hundred One" and "One Hundred and One":

"In British English it is pronounced "one/a hundred and one", in American English "one/a hundred one", or "one oh one" in both."

Wikipédia only accepts it under One Hundred One, and I'm sure others do it the same way.

Although people sometimes seem to use that (or 1001) to count by 'acurate' seconds....

But getting back to the riddle, I was so happy when looking at 0,1,2,3-- as their ending letters are 'e,o,e,o'-- then I realized that 3 isn't up there and that there are other letters involved in the ending. Plus, there'd be many more...

First letters of every word:
zotffsetffsssee

It sounds like it wants to be true!

Does it have anything to do with only a single letter from each of the numerals' words?
     The first letter?
     The last letter?
     A middle letter?

If not, does it have to do with two+ letters, but not all of the letters in the word?

If not, not, does it have to do with all of the letters in each word?

Should we use hyphens in, say, fourty-six?
     If so, are the hyphens relevant?

All of the letters in the word are relevant.

Hyphens... include them or don't, either way they aren't relevant.

Maybe if you add up all of the numerical values of the letters in each of the numerals, you get the same number?

Maybe if you add up all of the numerical values of the letters in each of the numerals, you get the same number?

Nice thought, but no.

Backtracking to the "and" debate, you're in my number riddle, and my way is to put "and" between "one hundred" and whatever the rest of the number is, so that's the way we do it in here. So nyah! 

... Eighty and six?

That would be silly.

Is we silly?

Yes. Yes you is.

Too... hard...!

92?

Grammar am for peoples who can't think for myself!

Hehe!

and a counter-argument:

apologies to those with 1024x768

One common thing about the numbers is that there are no repeated letters.

5000 (five thousend), unless you say thousend instead of one-thousend?

Sorry about all my deleated messages

...wow.  That's what the edit button is for, Red.

also, good job.  I think you have it

I cant let the answer be visible while checking if it is correct, or can I?

huh?

well, I mean, I had 24 up there but figured out it did not work

I was not sure, but was working on it and I figured I'd open a notepad instead

meh.  Personally, I would have had fun with leaving all of my wrong answers up.  It adds to the drama.

yeah, you are probably right

something like:
24
no, wait.  95
no... 67
wait! forget what I said before, it's 152!
sorry, that's wrong..

yeah, something like that was up there, just in letters

twenty four

no, that has two t's arrgggg, etc

I love python:

>>> for i in range(0,1000000+1):
...     s = int2word(i).strip()
...     if(len(s)==len(Set(s))):
...             print s

one
two
four
five
six
eight
ten
forty
forty six
sixty
sixty one
sixty four
eighty
eighty four
five thousand

And because my CPU needs more exercise, I'll just run it, this time without an upper bounds.

currently at 3.5 million and counting

9.6 million..

Bloody hell

82.5 million...

But all the millions, trillions, etc has two l's

I know.  Although this exercise proves a point, mostly I just want to see how far I can push my processor.

123.7 million...

both million, milliard, billion, billiard, trillion, trilliard, quadrillion, guintillion, sextilion, septillion, octillion, nonillion, decillion, undecillion, duodecillion, tredecillion, quattuordecillion, quindecillion, sexdecillion, septdecillion, octodecillion, novemdecillion, vigintillion and centillion has two l's

quit crushing my dreams!

A program written, millions listed...

We're no where closer to solving this are we?

so what number are you on now?

I might have solved it dek, but the answer is not confirmed yet. (I hope so anyway)

152.6 million... and I'm getting bored

I am on

nine-hundred-thousand-centillions-nine-hundred-thousand-vigintillions-nine-hundred-thousand-novemdecillions-nine-hundred-thousand-octodecillions-nine-hundred-thousand-septdecillions-nine-hundred-thousand-sexdecillion-nine-hundred-thousand-quindecillions-nine-hundred-thousand-quattuordecillions-nine-hundred-thousand-tredecillions-nine-hundred-thousand-duodecillions-nine-hundred-thousand-undecillions-nine-hundred-thousand-decillions-nine-hundred-thousand-nonillions-nine-hundred-thousand-octillions-nine-hundred-thousand-septillions-nine-hundred-thousand-sextilions-nine-hundred-thousand-guintillions-nine-hundred-thousand-quadrillions-nine-hundred-thousand-trilliards-nine-hundred-thousand-trillions-nine-hundred-thousand-billiards-nine-hundred-thousand-billions-nine-hundred-thousand-milliards-nine-hundred-thousand-millions-nine-hundred-and-ninetynine-thousand-nine-hundred-and-ninetynine.  

beat me that gotta be the longest word to

methinks you have a repeat character in there somewhere...

oh, no

of course not

what number comes after?

nine-hundred-thousand-centillions-nine-hundred-thousand-vigintillions-nine-hundred-thousand-novemdecillions-nine-hundred-thousand-octodecillions-nine-hundred-thousand-septdecillions-nine-hundred-thousand-sexdecillion-nine-hundred-thousand-quindecillions-nine-hundred-thousand-quattuordecillions-nine-hundred-thousand-tredecillions-nine-hundred-thousand-duodecillions-nine-hundred-thousand-undecillions-nine-hundred-thousand-decillions-nine-hundred-thousand-nonillions-nine-hundred-thousand-octillions-nine-hundred-thousand-septillions-nine-hundred-thousand-sextilions-nine-hundred-thousand-guintillions-nine-hundred-thousand-quadrillions-nine-hundred-thousand-trilliards-nine-hundred-thousand-trillions-nine-hundred-thousand-billiards-nine-hundred-thousand-billions-nine-hundred-thousand-milliards-nine-hundred-thousand-millions-one-million

depends on your system of names.  In mine, thousand-million>million>thousand>zero

all right.  I got bored and quit my program at 161.5 million

never seen that done before

?

thousand-million-millions, etc.

is that a number, or the right way to write out a number?

I dunno.  You wrote it.

of course you can get a higher one by using numbers

I prefer knuth up-arrow notation

I prefer smaler numbers (it does not take five minutes to say them out loud)

yeah, thats a good one, but it uses numbers, not letters

yeah, there is the I-have-to-spend-half-an-hour-explaining-how-awesomely-huge-this-number-is factor.

I'll make it easy:

∞

cheat.

besides, ∞ ∉ ℝ

yes of course, that made perfectly sense

enwhoiiieooiiinioiio

That's math speak for "Infinity's not a real number"

That doesn't even look like the 'not inclusive inside of-' (or whatever it's called) symbol!

-four?

[Ignore the fact that negative has 2 'e's!]

*grumble*brumble*unicode*grumble*brumble*

try copy/pasting it into word 2007.  it works for me

92? No

One common thing about the numbers is that there are no repeated letters. That's true.

5000  Is the answer I was looking for.

unless you say thousend instead of one-thousend  Personally, I would spell it five thousand... not five one thousand or anything funky like that

The rule in it's full form is that all the 16 numbers are positive integers, the English name for which contains no repeated letters.

Point goes to Red Wolf.

go wolfy!!

*kicks himself for missing what appears to be a simple answer*

all answers are obvious in hindsight

*kicks Sir M just because*

huh! that was totally uncalled for....

(solved)?

Yes. Yes it is.

ah, that felt GREAT!!

all answers are obvious in hindsight

Unless you are me....

*checks*

oh, thank god for that...i'm not you...

GRRRRRRRR

Who writes it one-thousend?

FAIL.

(I do realize that this is probably acceptable in some countries, but it isn't anywhere I've ever been...)