17576000 courses can be given unique catalog numbers.
There are three numbers and three English letters.
Each of three numbers can be chosen from 0 to 9, so the ways to choose each number is = 10
So the total number to choose three numbers = 10*10*10 = 1000
Each of letters can be chosen from A to Z.
Number of choice for the each letter = 26
So, the outcomes of letter combination = 26*26*26 = 17576
Hence the total possible catalog numbers = 1000*17576 = 17576000
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