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All integers ever tested in the Collatz problem eventually ends in the sequence 4-2-1.

Update: Starting with 6, or 12, will produce primes as well. E.g., 6 gives a Collatz trajectory of {6,3,10,5,16,8,4,2,1}, and 63105168421 is prime, etc. Can you find the next starting number that will produce a prime by concatenating the entire trajectory?


  Submitted: 1999-09-17 21:52:39;   Last Modified: 2016-08-01 08:12:32.

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