# Next in series.

What is the next number in the series : 1,2,4,8 ...
LVL 17
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IT Systems ManagerCommented:
16 - the next number is the previous number multiplied by 2.
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Author Commented:
Good try, but no, not that. ;)
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Saggar maker's framemakerCommented:
It could be 17 in that if you put the factors of 136 in numerical order you get 1, 2, 4, 8, 17 but there again that is not a proper series and indeed using that rule many numbers greater than  10 could be next.
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Commented:
We though this was a math problem, not a silly gotcha riddle.

With the information given, 16 is the only obviously correct answer and the only one you will get.

There are an infinite number of series that include 1, 2, 4, and 8.  I can define a curve that includes these four values and any other value.

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Author Commented:
Great math effort there ! Again, not the right answer this time. ;)
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Author Commented:

Err, this question is also in the Puzzles TA, so perhaps you don't need to be quite so dogmatic. You don't have to comment if you think the question is not worthy of your time and effort.
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Commented:
It is exactly like the puzzle: "Guess what I am holding in my hand?"  Do you want to play?
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Author Commented:
It is exactly like the puzzle: "Guess what I am holding in my hand?"  Do you want to play?

Those are two questions - simple maths at work there . . . so which one are you hoping to get an answer for?
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Author Commented:
We though this was a math problem, not a silly gotcha riddle.

There are no silly riddles, and in any case as I said beforehand, this question was also posted the the Puzzles TA.

I don't like being the butt of your misanthropic comments, so if it's all the same to you, I'll give in to your kiljoy manners, and delete the question without an answer. It's obvious that this is no place whatsoever for humour.
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Saggar maker's framemakerCommented:
Please confirm it is a series and not just a sequence of numbers.
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Commented:
This is a Math and Science Topic Area.  But you posted a question that looks like math and didn't tell us that it's a riddle until we answer.

So you get to say:  "Wrong"  "Wrong"  "Wrong"  "Wrong"  "Wrong"  "Wrong"

Isn't this fun?
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Commented:
I request that krakatoa post his answer to the riddle before closing the question unless it is the mod(9) thing.
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Author Commented:
Bye.
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Specialist 1Commented:
At this point with what we've been given there are two possible solutions for this set of numbers:1,2,4,8...
Solution 1:
2^0=1
2^1=2
2^2=4
2^3=8
2^4=16
Solution 1a:  Same answer of 16, but as stated above: Doubling the previous number.
1+1=2
2+2=4
4+4=8
8+8=16

Solution 2:
(1+2) +1=4
(2+4) +2=8
(4+8) +3=15

So 16 and 15 can potentially be used as the answer.
And also potentially any other variation can give other answers, but the answer most likely has to be greater than 8.
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Commented:
1, 2, 4, 8, 16  is the obvious 2^n answer for  n = 0, 1, 2, 3, ...

1, 2, 4, 8, 15  is also an excellent answer from (n³ + 5n + 6)/6  for  n = 0, 1, 2, 3, ...
This is the simplest polynomial that goes through the given points.
You can find a 4th degree polynomial that goes through these four and any fifth point.

1, 2, 4, 8, 6   is a possible answer that comes from  2^n (mod 10) for  n = 0, 1, 2, 3, ...
This is the same as taking the last digit of 2^n.

1, 2, 4, 8, 5   is another answer that comes from  2^n (mod 11) for  n = 0, 1, 2, 3, ...
There is no reason not to try another modulus.

1, 2, 4, 8, 7   is yet another answer that comes from  2^n (mod 9) for  n = 0, 1, 2, 3, ...
Since I got the points, this is probably what krakatoa was thinking about.
This is also what comes up if you Google "1 2 4 8"
If you think this is arbitrary, I would certainly have to agree.
Is there anything special or interesting about mod 9?
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Commented:
The answer could be literally anything.
Some of more easily justified ones include these:
https://oeis.org/search?q=1%2C2%2C4%2C8
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