# Multiplying by 2

1. May 14, 2005

### <<<GUILLE>>>

I guess most of you have come to this problem sometime, but this is my modern adaptation of it:

A member of physics forums bets with a moderator that he (the moderator) won't be able of multiplying his number of posts by two in the number of posts he (the normal member) has.

member's posts: 64

moderator's posts: 1

what moderator has to do: times his posts (1) by 2, 64 times.

After three decades the moderator accepts that it's impossible to achieve.

How many posts did the moderator have to do?

2. May 14, 2005

### BicycleTree

2^64, that's not even a puzzle. In the standard chessboard formulation of the problem it would be 2^65 - 1.

3. May 14, 2005

### <<<GUILLE>>>

ok, its not a puzzle, but its about math:

What I wanted you people to give me is the number 2^64 not tell me 2^64, I already said that!

4. May 14, 2005

### ArielGenesis

what so supprising with the 'number' of 2^64

5. May 14, 2005

### <<<GUILLE>>>

just that it's dificult to get: well, with a calculator it's easy, but you still have to multiply by tewo so many times, the numbr must be enormous. I just want to know it and knwo if there is someone that is so board that he has nothing better to do than this.

6. May 14, 2005

### BicycleTree

Step 1: Open microsoft calculator.
Step 2: Press the key labeled 2.
Step 3: Press the x^y key.
Step 4: Press the key 6
Step 5: Press the key 4.
Step 6: Press the key labeled =.
Step 7: Select "copy" from the Edit menu.
Step 8: Press ctrl-v in the Quick Reply window.

18446744073709551616

7. May 14, 2005

### theCandyman

What is the standard chessboard formula?

2^64 has about 20 digits, I doubt I could even name it correctly so I will not bother trying to write it out in its full glory.

Edit: I was correct, it did have 20 digits. Wow, what a useful little calculator!