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

[BR24]

What is the highest number you cannot make with the numbers 6, 9, or 20. Integers obviously. if you don't understand what i am asking, for example, you can't make 14, so which is the largest number you can't 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?

 

[gutti]

cant eventually make every number, still looking for prime numbers, largest is 2^43,112,609 − 1 so far i think.

 

[BR24]

dont think your right there, well don't 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.

 

[gutti]

Ah ok lol.

 

[BR24]

yeah haha so any clue how to do it?

 

[BR24]

can anyone confirm or disconfirm 43?

 

[mathman]

What is the highest number you cannot make with the numbers 6, 9, or 20. Integers obviously. if you don't understand what i am asking, for example, you can't make 14, so which is the largest number you can't 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?

What do mean by "make"? Are you talking about adding them together or multiplying or some other combination of arithmetic operations?

 

[BR24]

adding, corrected myself above.

 

[CRGreathouse]

http://mathworld.wolfram.com/McNuggetNumber.html
http://mathworld.wolfram.com/FrobeniusNumber.html
http://mathworld.wolfram.com/CoinProblem.html

 

[AUMathTutor]

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.