How many ways can we arrange 10 identical black balls and 10 identical red balls in a line, so that no ball has two neighbors that are of the same color?

**Clarification:** No ball (red or black) can be between two black balls or two red balls.

So, the following combinations aren't allowed for any three successive balls:

- BRB
- BBB
- RRR
- RBR

**Image credit:** https://www.dreamstime.com

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