Find the number of all whole numbers formed on the screen of a calculator which can be recognised as numbers with (unique) correct digits when they are read inverted. The greatest number formed onn its screen is 999999.

Explanation

To solve the problem of finding the total number of whole numbers that can be formed on a calculator screen and can be recognized as valid numbers when read inverted, we will categorize the numbers based on their digit lengths (1-digit, 2-digit, 3-digit, 4-digit, 5-digit, and 6-digit). The valid digits that can be used are 0, 1, 2, 5, 6, 8, and 9.

### Step-by-Step Solution:

1. **Identify Valid Digits**:
The valid digits that can be recognized when inverted are: 0, 1, 2, 5, 6, 8, 9. This gives us a total of 7 digits.

2. **Count 1-Digit Numbers**:
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