How to list files in a directory ending with number.csv



I am using the code
list.files("~/Development/glycoPipeApp/OUT/openMS/INPUT_DATA", pattern = ".csv")
and I get error $operator is not allowed for atomic vectors.

Additionally, I have some files name 1.csv, 2.csv ............. and I would like to make a regular expression that detects only files with number.csv ending. The number could be a digit or a 2 digits number and so on ....