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Derek's phone number, 336 - 7624, has the property that the three-digit prefix, 336, equals the product of the last four digits, 7 times 6 times 2 times 4. How many seven-digit phone numbers have this property?

 Dec 24, 2021
 #1
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There are 84300 phone numbers with this property.

 Dec 24, 2021
 #2
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A short computer code in C++ shows that there are:

 

2,530 such telephone numbers.

 Dec 25, 2021

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