Keyboards 2321

Miško had small keys on the shelf, which you can see in the picture. Their tones were marked on the white keys. Little Klára found the keys. As she took them off the shelf, they fell out of her hand, and all the white keys spilled out. So that the brother would not be angry, Klára started to put them back together. At the same time, she noticed that they could only be inserted in certain places, as they were hindered by the black keys placed exactly in the middle between the two white ones. Klára managed to fold the keyboards somehow, but the tones on them were mixed because she did not yet know the musical scale. Find out how many ways Klára could have composed the keys. ..?

Correct answer:

n =  23

Step-by-step explanation:

n=2 2 61=23

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