Chemical Abstracts Service Registry. A registry of unique numeric identifiers allocated to each substance. A CAS Registry Number (abbreviated CASN, CASRN or CAS#) can contain up to 10 digits, divided by hyphens into 3 parts. The first part of the number has up to 7 digits; the second part has 2 digits, and the final part consists of a single check digit used to verify by computer the validity and uniqueness of the entire number. The full CAS Registry can be searched from different online sources.

Source: https://ec.europa.eu/

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