Which of the following is a proper integer number (in the “C” language sense)?

In C, a proper integer number is a sequence of digits without any separators such as commas, decimal points, or underscores. Based on this, let’s evaluate the provided options:

1. 123456: This is a proper integer number.
2. 123,456: This is not a proper integer number because it contains a comma.
3. 123.456: This is not a proper integer number because it contains a decimal point.
4. 123_456: This is not a proper integer number because it contains an underscore.

Therefore, the proper integer number in the “C” language sense is 123456.