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Highest number impossible to make with 6,9,20.

  1. Mar 26, 2009 #1
    What is the highest number you cannot make with the numbers 6, 9, or 20. Integers obviously. if you dont understand what i am asking, for example, you cant make 14, so which is the largest number you cant make since once you get so high you can make every number. Is there a quick or mathematical way to do this besides brute force and guessing?
  2. jcsd
  3. Mar 26, 2009 #2
    cant eventually make every number, still looking for prime numbers, largest is 2^43,112,609 − 1 so far i think.
  4. Mar 26, 2009 #3
    dont think your right there, well dont think i stated the answer clear enough. you have to add, use their sums, not multiply. I know for a fact that the answer is below one million.
  5. Mar 26, 2009 #4
    Ah ok lol.
  6. Mar 26, 2009 #5
    yeah haha so any clue how to do it?
  7. Mar 26, 2009 #6
    can anyone confirm or disconfirm 43?
  8. Mar 26, 2009 #7


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    What do mean by "make"? Are you talking about adding them together or multiplying or some other combination of arithmetic operations?
  9. Mar 26, 2009 #8
    adding, corrected myself above.
  10. Mar 26, 2009 #9


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  11. Mar 26, 2009 #10
    If you think it's under 1,000,000, just write a computer program to start generating numbers, sort the list, and look for a sequence of at least 6 consecutive numebrs. Clearly, you can make any number after that... since you just add 6 to one of those numbers.
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