# Quick Number Puzzle
**URL:** https://boards.straightdope.com/t/quick-number-puzzle/364240
**Category:** In My Humble Opinion
**Created:** [July 12, 2006, 9:18pm UTC](https://boards.straightdope.com/t/quick-number-puzzle/364240 "2006-07-12T21:18:20Z")
**Posts on this page:** 20
**Page:** 1
### Author:  [@Asimovian](https://boards.straightdope.com/u/Asimovian)
#### Post date: [July 12, 2006, 9:18pm UTC](https://boards.straightdope.com/t/quick-number-puzzle/364240/1 "2006-07-12T21:18:20Z")
I had the following on a daily calendar I use, but I arrived at my answer differently than they did:
> [@Puzzle Calendar](#):
>
> Find the number that best completes the sequence below.
>
> 19 - 37 - 55 - 73 - 9?
I’m just curious to see if the rest of you come up with their answer or mine.
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### Author:  [@Stainz](https://boards.straightdope.com/u/Stainz)
#### Post date: [July 12, 2006, 9:23pm UTC](https://boards.straightdope.com/t/quick-number-puzzle/364240/2 "2006-07-12T21:23:24Z")
I get 91. The numbers in the sequence go up by 18.
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### Author:  [@Jayn\_Newell](https://boards.straightdope.com/u/Jayn_Newell)
#### Post date: [July 12, 2006, 9:33pm UTC](https://boards.straightdope.com/t/quick-number-puzzle/364240/3 "2006-07-12T21:33:08Z")
Same answer as Stainz, different reasoning.
Each pair of numbers adds up to 10
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### Author:  [@Asimovian](https://boards.straightdope.com/u/Asimovian)
#### Post date: [July 12, 2006, 9:34pm UTC](https://boards.straightdope.com/t/quick-number-puzzle/364240/4 "2006-07-12T21:34:03Z")
I should have said, I want to see if you come up with the same rationale that they used.
At any rate, Stainz, you came about it the same way I did. However, their explanation…
…was much simpler: “Two series. 1, 3, 5, 7, 9 and the same sequence reversed.” I didn’t notice that pattern at all until reading their solution.
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### Author:  [@Robot\_Arm](https://boards.straightdope.com/u/Robot_Arm)
#### Post date: [July 12, 2006, 9:37pm UTC](https://boards.straightdope.com/t/quick-number-puzzle/364240/5 "2006-07-12T21:37:43Z")
The first thing I thought of was…a palindrome. The same sequence backwards and forwards, the last number has to be 1.
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### Author:  [@Asimovian](https://boards.straightdope.com/u/Asimovian)
#### Post date: [July 12, 2006, 9:39pm UTC](https://boards.straightdope.com/t/quick-number-puzzle/364240/6 "2006-07-12T21:39:38Z")
> [@Jayn\_Newell](#):
>
> Same answer as Stainz, different reasoning.
>
> Each pair of numbers adds up to 10
Huh…didn’t even think of that one, although that’s closer to what the calendar’s answer is.
**Robot Arm** , apparently you should be authoring these puzzles. 😃
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### Author:  [@ultrafilter](https://boards.straightdope.com/u/ultrafilter)
#### Post date: [July 12, 2006, 9:44pm UTC](https://boards.straightdope.com/t/quick-number-puzzle/364240/7 "2006-07-12T21:44:35Z")
I get 91, because the first difference is constant (basically the same as what **Stainz** said, but with extra jargon).
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### Author:  [@Otto](https://boards.straightdope.com/u/Otto)
#### Post date: [July 12, 2006, 9:45pm UTC](https://boards.straightdope.com/t/quick-number-puzzle/364240/8 "2006-07-12T21:45:11Z")
Without looking at the other answers:
the next number is 1. The first number is decreasing by 2 and the second number is increasing by 2. You could do a more complicated solution, like the first number increases by 2 and the first plus the second number = 10.
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### Author:  [@Otto](https://boards.straightdope.com/u/Otto)
#### Post date: [July 12, 2006, 9:50pm UTC](https://boards.straightdope.com/t/quick-number-puzzle/364240/9 "2006-07-12T21:50:13Z")
Hey, I got the right answer _and_ a unique solution! Yay me! I never get these.
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### Author:  [@Left\_Hand\_of\_Dorkness](https://boards.straightdope.com/u/Left_Hand_of_Dorkness)
#### Post date: [July 12, 2006, 10:07pm UTC](https://boards.straightdope.com/t/quick-number-puzzle/364240/10 "2006-07-12T22:07:34Z")
**Asimovian** , I solved it the same way you did. I think your strategy is the first one I try with any sequence puzzle.
Daniel
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### Author:  [@Spidey](https://boards.straightdope.com/u/Spidey)
#### Post date: [July 12, 2006, 10:26pm UTC](https://boards.straightdope.com/t/quick-number-puzzle/364240/11 "2006-07-12T22:26:33Z")
i got it by doubling the number, then adding the previous. eg 73 = 2 x 55 - 37
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### Author:  [@Asimovian](https://boards.straightdope.com/u/Asimovian)
#### Post date: [July 12, 2006, 10:36pm UTC](https://boards.straightdope.com/t/quick-number-puzzle/364240/12 "2006-07-12T22:36:23Z")
> [@Spidey](#):
>
> i got it by doubling the number, then adding the previous. eg 73 = 2 x 55 - 37
Wow…that’s a different one – I like it! 🙂
How would you get the second number in the sequence, though? In other words, 37 = 2 x 19 - ??
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### Author:  [@photopat](https://boards.straightdope.com/u/photopat)
#### Post date: [July 12, 2006, 10:42pm UTC](https://boards.straightdope.com/t/quick-number-puzzle/364240/13 "2006-07-12T22:42:45Z")
without looking at anybody else’s reply, the final number is 91, which makes the series a palindrome.
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### Author:  [@Robot\_Arm](https://boards.straightdope.com/u/Robot_Arm)
#### Post date: [July 12, 2006, 10:46pm UTC](https://boards.straightdope.com/t/quick-number-puzzle/364240/14 "2006-07-12T22:46:20Z")
I like the cut of your jib, **pat**.
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### Author:  [@iamthewalrus\_3](https://boards.straightdope.com/u/iamthewalrus_3)
#### Post date: [July 12, 2006, 11:14pm UTC](https://boards.straightdope.com/t/quick-number-puzzle/364240/15 "2006-07-12T23:14:25Z")
I also jumped to the palindrome solution. Normally I’ll first check first and second differences for these, but this one was so obviously a palindrome.
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### Author:  [@Tyrrell\_McAllister](https://boards.straightdope.com/u/Tyrrell_McAllister)
#### Post date: [July 13, 2006, 12:20am UTC](https://boards.straightdope.com/t/quick-number-puzzle/364240/16 "2006-07-13T00:20:30Z")
I got the same answer as everyone else, but with different reasoning.
I couldn’t help but notice that the first four terms are the values of
n^5 - 15n^4 + 85n^3 - 225n^2 + 292n - 199
for n = 1, 2, 3, 4. Evaluating at n=5 gives 91.
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### Author:  [@Thudlow\_Boink](https://boards.straightdope.com/u/Thudlow_Boink)
#### Post date: [July 13, 2006, 1:34am UTC](https://boards.straightdope.com/t/quick-number-puzzle/364240/17 "2006-07-13T01:34:06Z")
My first thought was the same as **Robot Arm** ’s. After looking for an alternative solution, I came up with **Stainz** ’s.
But before any of that, I was thrown off a little because, technically, what we’re finding is not a _number_ but a _digit_. If we really were looking for the next _number_ in the sequence 19 - 37 - 55 - 73 - 9, some of these solutions (like **Stainz** ’s), won’t work.
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### Author:  [@Little\_Nemo](https://boards.straightdope.com/u/Little_Nemo)
#### Post date: [July 13, 2006, 2:04am UTC](https://boards.straightdope.com/t/quick-number-puzzle/364240/18 "2006-07-13T02:04:36Z")
I also figured that the first four numbers were
1x18+1
2x18+1
3x18+1
4x18+1
and the next one should be
5x18+1
but like Thudlow, I missed that the question was asking for a digit not a new number.
I also missed
the palindrome pattern
Did anyone come up with a different answer?
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### Author:  [@audiobottle](https://boards.straightdope.com/u/audiobottle)
#### Post date: [July 13, 2006, 3:22am UTC](https://boards.straightdope.com/t/quick-number-puzzle/364240/19 "2006-07-13T03:22:33Z")
I got to the 9? at the end and thought, huh? But I did the same as other people. I found the constant difference to be 18. Then I noticed that it was a palindrome.
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### Author:  [@Chanteuse](https://boards.straightdope.com/u/Chanteuse)
#### Post date: [July 13, 2006, 3:37am UTC](https://boards.straightdope.com/t/quick-number-puzzle/364240/20 "2006-07-13T03:37:32Z")
> [@Otto](#):
>
> Hey, I got the right answer _and_ a unique solution! Yay me! I never get these.
Cool! This is how I figured it out, too–but you were still first! 🙂
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