Calc: What are the numbered columns to the left of row numbers? How do I hide them?

LibreOffice (en_us)

Certain rows have “-” and “+” buttons that hide and unhide their rows. How did LO determine which rows should have these buttons? How do I control that?

LO extra columns.png

(Edit: activated screenshot -AK)

Try ‘Data’ > ‘Group and Outline’

Thank you, that did the trick. And now I know where to look in Help to see what ‘Group and Outline’ does!