Jesse has ten squares, which are labeled . In how many ways can he color each square either red, green, yellow, or blue such that for all , if divides , then the -th and -th squares have different colors?
Problem 1474
Official solution
To solve this problem, we need to ensure that for all , if divides , then the -th and -th squares have different colors. We will use a step-by-step approach to count the number of valid colorings.
1. Color the 1st square:
- There are 4 possible colors for the 1st square.
2. Color the 7th square:
- The 7th square is not influenced by any other square because 7 is a prime number and does not divide any other number in the set . Thus, there are 3 remaining colors for the 7th square.
3. Color the remaining squares:
- We need to consider the squares that are influenced by the divisibility condition. These squares are .
4. **Casework on :**
- We will consider different cases based on the colors of squares .
**Case 1: and :**
- There are 3 choices for the color of square 2.
- There are 2 choices for the color of square 3 (since it must be different from square 2).
- There are 2 choices for the color of square 5 (since it must be different from square 2).
- Thus, there are ways to color squares .
**Case 2: :**
- There are 3 choices for the color of square 2 (which also determines the color of square 3).
- There are 2 choices for the color of square 5.
- Thus, there are ways to color squares .
**Case 3: :**
- There are 3 choices for the color of square 2 (which also determines the color of square 5).
- There are 2 choices for the color of square 3.
- Thus, there are ways to color squares .
**Case 4: :**
- There are 3 choices for the color of squares .
- Thus, there are ways to color squares .
5. **Color the remaining squares :
- For each of the above cases, we need to ensure that the remaining squares are colored such that the divisibility condition is satisfied.
- For each case, we have:
- 1 choice for square 4 (since it must be different from square 2).
- 1 choice for square 6 (since it must be different from squares 2 and 3).
- 1 choice for square 8 (since it must be different from square 4).
- 1 choice for square 9 (since it must be different from square 3).
- 1 choice for square 10 (since it must be different from squares 2 and 5).
6. Total number of ways:**
- Summing up the number of ways for each case:
- Case 1: ways
- Case 2: ways
- Case 3: ways
- Case 4: ways
- Total: ways
7. Multiplying with the factors we ignored:
- We initially ignored the factors for coloring the 1st and 7th squares.
- Thus, the total number of ways is .
The final answer is .