what is the next number in this series

3      -6      12      4      20   ?
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 3 -  9 = -6
-6 + 18 = 12
12 -  8 =  4
 4 + 16 = 20
20 -  7 = 13
13 + 14 = 27

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Or maybe it is something else.
There is really no way to tell.

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next number is 13, working out can be provided
An alternate solutionEquivalent to 4th degree polynomial passing through the given points.
The next point can be any value you like, and you can find a 5th degree polynomial that will pass through them all.  That gives an infinite number of solutions that pass through the first five points.  And there are infinities of infinities more.
davmayrAuthor Commented:
I went with 13 before you guys answered. Thank you for the confirmation. BTW, I appreciate your speedy answers
Here is the polynomial . . . .
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Math / Science

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