Starting with 2, how long can you keep multiplying it by 2 in your head? So your answers will go- 4, 8, 16, 32 etc. Nothing but your mind is allowed though when you start to struggle jot down the last number so you can check it was correct later. Once you have written it down look away immediately since staring at it will help get the next and is cheating. Alternatively use a calculator (10 digit or more) and type 2x2 and = then keep pressing = after each calculation and check occasionally.
How far can you go?

What's after 4?

I got to 4096, then didnt feel like doing math. On spring break ya know
2, 4, 8, 16, 32, 64, 128, 256, 512, 1024, 2048, 4096.

Kinda far i guess.

During my Biology class, the other kids used a calculator to find out how many bacteria there will be in 120 minutes if 1 bacteria split every ten minutes; while all the other kids did this, I used my brain without any paper!
1, 2, 4, 8, 16, 32, 64, 128, 256, 512, 1024, 2048, 4096, 8192, 16384

*The one is there only because that's how I counted in Bio*
PS. I know that I went further than the true number of cells; I was just testing how far I can go

2,4,8,16,32,64,128,256,512,1024,2048,4096,8192,16384,32768,65536,131072,262142,524284...

I'm not going further coz i'm busy right now but I have a method that works for a LOT of digits, which actually consists in multiplying from left to right (this is the only occasion i multiply from left to right, but for memory it's good)

- Greg

I made it to 32768, but I'm sure I can go further just in my head.

I have up to 2^13 memorized. Starting from there, I got up to 2^20 before I could not keep track of the numbers.

It's easier if you do the mental arithmetic in binary notation:

1
10
100
1000
.
.
.

Oops: 131072,262142

I've had up to 262144 memorized since middle school

As a digital circuit designer I have become accustomed to converting binary numbers up to 16 bit to hex and decimal without a calculator. I have all the powers of 2 in my head up to 2^16 an I can add them in my head too, up to 1111,1111,1111,1111 = 0xFFFF = 65535. It all falls apart for numbers with more than 16 bits. I have to use calculator for that.

I "discovered" this game when I was in 3rd grade. I added 1 to itself to get 2, added to 2 itself to get 4, ... it astounded me how quickly the numbers got big. I was so amazed I got up in front of my class to tell everyone about my incredible discovery. I think I was able to get up to 2^16 or so at the time. Prepared me well for computers later.

2, 4, 8, 16, 32, 64, 128, 256, 512, 1024, 2048, 4096, 8192, 16384, 32768, 65536
I don't feel like continuing on after that, though I could.

2 4 8 16 32 64 138 276


thats all i can do with less than 10 seconds of thinking per number

You might want to stick to 64 or less...

I'm one of the 16 bit guys. Sorry but I've already done my share of memorization on this and after 66536 it's pretty insane to keep doing it in your head.

This was an interesting exercise I had never tried before without a calculator. I was able to get to 524,288, and then I was just unable to continue keeping all numbers in my mind at the same time (which was kind of frustrating when I realized the number were just dissapearing from my working memory!)

Cheers!

Weird, I used to do this in my head back in grade school. I think I stopped at 65536 not even realizing it was 2^16. Maybe now I should just remember the next one is 131072.

-d

2
4
8
16
32
64
128
256
512
1024
2048
4096
8192
16384
32768
65536
131072
262144
524288
1048576
2097152
Wow I'm even surprised!