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Each CAS Registry Number:

• Is a unique numeric identifier
• Designates only one substance
• Has no chemical significance
• Is a link to a wealth of information about a specific chemical substance

A CAS Registry Number is unique and specific to only one substance regardless of how many other ways the substance can be described (e.g., molecular formula, structure diagram, systematic names, generic names, proprietary or trade names, trivial names.

The CAS RN can be found in searching SciFinderⁿ, STN databases, Chemical Abstract Society publications, governmental agency publications, some Elsevier databases.

Source: https://www.cas.org/support/documentation/chemical-substances/faqs