Here is a brain game that we used to play in our school days. It was pretty confusing to make when the numbers get larger. Here is the basic simple 10 digit version with the medium one that is 55 digit version.
If you show this trick to a friend they will think you are pretty awesome psychic.
Theme of the game:
You tell a friend to think of a number and remember it.
Then you show some sheets with numbers and ask them if the number they are thinking of exists in those sheets.
After all the sheets are done. You do some psychic things and declare the number.
They are in awe!
Step 1: How to Make the Sheets (small One)
For a 10 digit game you take 4 sheets of paper. Why 4 sheets! Because 1+2+3+4 = 10.
Mark them 1 to 4
Now start adding numbers
1 goes in sheet 1(simple)
2 goes in sheet 2(simple)
3 goes in sheet 3(simple)
4 goes in sheet 4 (simple)
5 goes in (sheet 1 and sheet 4) or (sheet 2 and sheet 3) (1+4=5) or (2+3=5)
6 goes in (sheet 2 and sheet 4) or (sheet 1 sheet 2 and sheet 3) (2+4=6) or (1+2+3=6)
7 goes in (sheet 3 and sheet 4) or (sheet 1 sheet 2 and sheet 4) (3+4=7) or (1+2+4=7)
8 goes in (sheet 1 sheet 3 and sheet 4) (1+3+4=8)
9 goes in (sheet 2 sheet 3 and sheet 4) (2+3+4=9)
10 goes in (sheet 1 sheet 2 sheet3 and sheet 4) (1+2+3+4=10)
Pretty simple thing! The pdf is added if you want one!
Step 2: How to Make the Sheets (large One)
The large sheet can be made in the same manner! Just that you use 10 sheets for 55 numbers
the pdf of a perfectly created sheet is given here. Just print cut and play along. You can of-course make one by hand to make one.
Step 3: How to Play
Wear a turban and look like an Indian sadhu (that is optional)
Have the different sheets sequenced
Ask your friend to memorize a number between 1 to 55 (1 to 10 if you are using the small version).
When they are done!
Show them the sheets one by one (asking "is your number in this piece of paper)
You start adding the numbers on the heading of the sheet.
If your friend says yes, you add the number.
If your friend says no, leave the sheet (don't add the sheet number).
When all the sheets are done! The number you have summed up is the number your friend have thought of.
If your friend have said yes for sheets 4, 5, 7 and 10 then the number you get is (4+5+7+10=26) 26 that your friend has thought off.
Pretty simple thing.