The decimal part of the number (when divided by 7)  has a strict period. This period shifts, but the sequence of figures does not change.

I selected three numbers in different colors. These numbers must be remembered.

Example (Divide the number by 7):

• If the first digit after the comma is 4, then next will go 285714... etc.
• If the first digit is 5, then then next will go 7142857... etc.