.R21 File Extension
File TypeWinRAR Split Archive Part 21
What is an R21 file?
File created as part of a multi-volume compressed .RAR archive; stores part 21 of a compressed, split archive; used for reconstructing an original file with the other split archive parts.
RAR multi-volume archives are created using the extensions ".r00" through ".r99," where the digits represent the archive file sequence. Therefore, R21 is actually the 22nd part of the split archive.