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How many arrangements of the numbers 1, 2, 3, ..., 7, 8, 9 are there where the sum of any two adjacent numbers is odd?

 Aug 6, 2022
 #1
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It seems like swapping the even numbers around with eachother would do the trick. In this series there are 4 even numbers, they can be rearranged in 4! ways or 4x3x2x1 = 24.

 Aug 6, 2022
 #2
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See this link:   https://web2.0calc.com/questions/counting_92640

 Aug 6, 2022

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