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## Main Question or Discussion Point

In the text, there is a rubber band model for 1D chain of N links. Assume each link of the rubber band is align horizontally either to the right or to the left. In the text, define [tex]N_+[/tex] as the number of links directed to the right and [tex]N_-[/tex] represents the number of links directed to the left. I think the total configuration of the system should be

[tex]\Omega = \frac{N!}{N_+!N_-!}[/tex]

but it is

[tex]\Omega = \frac{2N!}{N_+!N_-!}[/tex]

I wonder where is the "2" come from?

[tex]\Omega = \frac{N!}{N_+!N_-!}[/tex]

but it is

[tex]\Omega = \frac{2N!}{N_+!N_-!}[/tex]

I wonder where is the "2" come from?