This is a picture from my sheet for Chopin's Nocturne in F minor, Op. 55, No. 1. I don't understand what the number next to this note means.
It's just a fingering. It shows you that you need to play C with the 3rd finger and thus Ab* with the 1st one. You'd also play the low F with your pinky (5th finger).
It's quite common to include the fingerings in pieces; it's a way to help the player. Usually, you'd find the numbers on top of the note.From the link I'm providing below, you can see that:
The author here mentions fingerings in different parts and above the notes, but the logic of it is the same. Also, from this extract of the piece you can see that there is nothing fishy going on before or after the part you asked about (5th bar in my pic) and that it's simply a fingering.
* I'm saying Ab, because the piece is in F minor