The R2 in onsemi suffixes is calling out tape and reel packaging, typically quantities of 2,500 or 4,000 which Digi-Key receives from the manufacturer. These will be cut down into smaller quantities if ordering Digi-Reel or Cut-Tape packaging.
LM2904DR2G is an example part number.
See Also:
Onsemi Tape and Reel Packaging Standards