There have been 1383 UK chart single number 1s since 1952.
This is a serious song by ABBA, probably a turning point in their career. You can see a definite transition in ABBA's sound here as they are beginning to leave the Bubblegum behind and start touching on serious issues, such as divorce. One can't help but wonder if there was a foreshadowing of the divorces that would end up splitting the group up just a short few years later.
More songs from the same decade.