Asked by sub to AntsPiano on yt
Find the total number of three-digit prime numbers that can be formed using the digits 1, 7 and 9. You may repeat digits.
Answers
Answered by
oobleck
There are only 3^3 = 27 numbers to choose from:
111, 117, 119, ... 991, 997, 999
So check each for primality.
since 111 = 3*37, none of the numbers 111,333,999 can be prime
Maybe you can think of some other shortcuts, such as casting out 3's or 9's.
111, 117, 119, ... 991, 997, 999
So check each for primality.
since 111 = 3*37, none of the numbers 111,333,999 can be prime
Maybe you can think of some other shortcuts, such as casting out 3's or 9's.
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