NO No No!
That is a Row number (you can even turn it OFF. Preferences: behavior: Show row numbers: remove tick)
Your metadata is in a terrible mess
Regardless of what you may have received in the book or downloaded, YOU need to make it uniform (at least within groupings of books) so you can group
Downloads are no solution: Author names vary, depending on who mad the source. I see the SAME Author with and with out middle initial And With or without a . or space AND even sometime a full middle name (even if that has NEVER appeared on the cover
) Pick how you want it and make ALL usage the same
I saw easily 2 variations of what I believe (I am a English only user
) is a series or magazine issue
Make those all look the same way. Use standard Calibre columns when possible, removing series info from a title when possible (it may ALSO appear in the series column), because the title may only be Title 2 which is the same series as Title 1. The series would be Title [1],Title [2]
You sort on Series to get the order (you can NOT sort an index by itself as someone suggested)
See the 2 attachments. 1 is unsorted (the way it was added to the Library), the other sorted by Issue (series) I used a Magazine to show a way to deal with titles that do not vary normally.