To help me find the exact paper, could you clarify the (e.g., computer science, chemistry, law) or where you first encountered the code? Based on that, I can provide a more targeted search .

: This is a specific international standard regarding Water quality — Determination of the dissolved fraction of selected active pharmaceutical ingredients . If your topic is environmental science, the ISO 21676 standard is the definitive "paper" on this topic.

It is possible the string is part of a DOI (Digital Object Identifier) or a specific database ID. For example:

: In some cases, strings like "21676" appear in FFmpeg or HandBrake logs when processing video. 3. Potential Misspelling or Truncation

If the term refers to the MP4 container or a specific encoding, you might be looking for papers on the standard.

: A paper ID like 2106.076... might be what you're recalling.