To make the bar numbers invisible (hide them):

\layout {
\context {
\Score
\remove "Bar_number_engraver"
}
}

Sometimes I want all bar numbers to be visible (show them), especially when putting the lyrics on the melody:

In the melody, insert:
\override Score.BarNumber
#'break-visibility = #end-of-line-invisible

To check the bar number in the editor, place the following before the bar in question:
\barNumberCheck #1 % (put any number here)