Question 1210184
Let's break down this problem into two cases based on the given condition.

**Case 1: The first three digits equal the next three digits.**

1.  **First three digits:** Since the first digit cannot be 0, there are 9 choices for the first digit (1-9). For the second and third digits, there are 10 choices each (0-9).
    * Number of choices for the first three digits: 9 * 10 * 10 = 900
2.  **Next three digits:** These digits must be the same as the first three digits, so there's only 1 choice for each of these three digits.
    * Number of choices for the next three digits: 1
3.  **Last digit:** There are 10 choices for the last digit (0-9).
    * Number of choices for the last digit: 10
4.  **Total numbers in Case 1:** 900 * 1 * 10 = 9000

**Case 2: The first three digits equal the last three digits.**

1.  **First three digits:** Same as Case 1, there are 900 choices.
    * Number of choices for the first three digits: 900
2.  **Next digit:** There are 10 choices for the next digit (0-9).
    * Number of choices for the next digit: 10
3.  **Last three digits:** These digits must be the same as the first three digits, so there's only 1 choice for each of these three digits.
    * Number of choices for the last three digits: 1
4.  **Total numbers in Case 2:** 900 * 10 * 1 = 9000

**Overlapping Case**

We've counted the numbers where the first three digits are equal to both the next three and the last three twice (e.g., 123-123123). We need to subtract these numbers once to avoid overcounting.

1.  **First three digits:** 900 choices.
2.  **Next three digits:** 1 choice.
3.  **Last three digits:** 1 choice.
4.  **Total numbers in the overlap:** 900 * 1 * 1 = 900

**Final Calculation**

* Total numbers = (Numbers in Case 1) + (Numbers in Case 2) - (Numbers in the overlap)
* Total numbers = 9000 + 9000 - 900 = 17100

**Therefore, you can remember 17,100 seven-digit telephone numbers.**