1. Choose a number between 800 and 810.
2. Square the last two digits:
   _ _ _ _ X X
3. Multiply the last two digits by 16
   (keep the carry): _ _ X X _ _
4. Square 8, add the carry: X X _ _ _ _

   Example:

1. If the number to be squared is 802:
2. Square the last two digits:
   2 × 2 = 4: _ _ _ _ 0 4
3. Multiply the last two digits by 16:
   16 × 2 = 32: _ _ 3 2 _ _
4. Square 8: 6 4 _ _ _ _
5. So 802 × 802 = 643,204.

   See the pattern?

1. If the number to be squared is 807:
2. Square the last two digits:
   7 × 7 = 49: _ _ _ _ 4 9
3. Multiply the last two digits by 16
   (keep the carry): 16 × 7 = 112: _ _ 1 2 _ _
4. Square 8, add the carry (1): 6 5 _ _ _ _
5. So 807 × 807 = 651, 249.