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Lê Quốc Trần Anh Coordinator

25/06/2018 at 03:08
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A “deletable prime” is a positive integer that (1) is prime and (2) is either a onedigit integer or, after removing one digit, results in another deletable prime. For example, 439 is deletable because 439 is prime and deleting the 9 results in another deletable prime, 43, which is deletable because removing the 4 results in the prime 3. What is the smallest deletable prime larger than 443?  



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    Tôn Thất Khắc Trịnh 25/06/2018 at 04:40

    447 is not prime because it's divisible by 3
    449 is prime but it's not deletable
    451 is not prime because it's deivisible by 11
    453 is not prime because it's divisible by 3
    457 is prime. If you remove the digit "5", you'll get 47, which is prime, then you can remove "4" to get the prime number 7. So the anser is 457

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    Tôn Thất Khắc Trịnh 25/06/2018 at 04:41

    Sorry, accidentally type deivisible, it's *divisable



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