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No primes 2 (Posted on 2011-07-29) Difficulty: 2 of 5
Prove that no number in the sequence 371, 3711, 37111... is prime.

  Submitted by Math Man    
Rating: 4.0000 (1 votes)
Solution: (Hide)
If the number of 1's is divisible by 3, then it is divisible by 37. If the number of 1's is 1 mod 3, then the number of 1's is either 1 or 4 mod 6. If it is 1 mod 6, then the number is divisible by 7. If it is 4 mod 6, then the number is divisible by 13. If the number of 1's is 2 mod 3, then it is divisible by 3. Therefore, no number in the sequence 371, 3711, 37111... is prime.

Comments: ( You must be logged in to post comments.)
  Subject Author Date
Solution37 &38 - UNIQUE NUMBERS - SPOILERAdy TZIDON2011-07-29 11:45:07
No SubjectAdy TZIDON2011-07-29 11:43:01
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