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More ways to get Braingle...

2, 5, 12, 31, 86....

Series teasers are where you try to complete the sequence of a series of letters, numbers or objects.

 

Puzzle ID:#3752
Fun:*** (2.18)
Difficulty:*** (2.38)
Category:Series
Submitted By:cathalmccabe***
Corrected By:shenqiang

 

 

 



What's the next number in this sequence?

2, 5, 12, 31, 86....

246
249
252
255
258



Answer

The answer is 249.

3^0 + 1 = 2
3^1 + 2 = 5
3^2 + 3 = 12
3^3 + 4 = 31
3^4 + 5 = 86
3^5 + 6 = 249

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Comments

jdnorway
May 03, 2002

No, it's 249.
chamber44
May 20, 2002

I might have gotten the answer if it was listed. The CORRECT answer is 249. Quit posting without double checking your work. 3^3+4=31 NOT 86. And 3^4+5=86 NOT 248. JDNOWAY is right.
mad-adeAhu*
Jun 29, 2002

I agree with the others this is a poor example of posting any old rubbish.
(user deleted)
Aug 31, 2002

It appears that cathalmcabe is well adept at posting any old rubbish. almost all his teasers i have seen up to date are either totally incorrect of contain disputable facts.
mathemagicianus*
Apr 26, 2008

2, 5, 12, 31, 86, ...

The differences {a2-a1, a3-a2,a4-a3,a5-a4,...} = {3, 7, 19, 55,... }

Now, {b2-b1, b3-b2, b4-b3} =
{4, 12, 36, ... }
The last sequence is geometric with r=3, making the next term 108. Hence, b5-b4 = 108 ; b5= 163; a6-a5 = 163 , or a6 = 249.
dalfamnestAnz*
Aug 24, 2010

With the correction, it's not so bad! I worthwhile little challenge. You can also get the next number using "x3 -1", "x3 -3", "x3 -5", etc
Quocalimar*
Feb 16, 2013

i did this to get 258.
the final number times 2, plus the number before it.
Odd coincidence, or did you plan that?
spikethru4*au*
Feb 17, 2013

Quocalimar, that doesn't even work. 2 x 86 + 31 = 203. Neither does it hold for the other numbers in the sequence.

Or am I misunderstanding you completely?
eighsseAus*
Aug 25, 2013

Good one, I got it after the hint. Except I figured it this way, 3x-1, 3x-3, 3x-5, 3x-7....

Where x is each new number progressively.



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