4!
Four factorial.
4 * 3 * 2
= 24 permutations
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10 x 9 x 8 = 720 different "permutations"
There are 720 possible permutations.
Since there are no duplicate letters in the word RAINBOW, the number of permutations of those letters is simply the number of permutations of 7 things taken 7 at a time, i.e. 7 factorial, which is 5040.
There are 330 possible 5 note permutations derived from the chromatic scale.