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

Guest Aug 6, 2022

#1**+1 **

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.

tuffla2022 Aug 6, 2022