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

1. Mar 26, 2009

### BR24

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. Mar 26, 2009

### gutti

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

3. Mar 26, 2009

### BR24

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.

4. Mar 26, 2009

### gutti

Ah ok lol.

5. Mar 26, 2009

### BR24

yeah haha so any clue how to do it?

6. Mar 26, 2009

### BR24

can anyone confirm or disconfirm 43?

7. Mar 26, 2009

### mathman

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

8. Mar 26, 2009