https://doi.org/10.1351/goldbook.D01569
The number of @M04018@ in a @M03667@ or @O04286@, a @B00682@ or a @C00946@.
Source:
PAC, 1996, 68, 2287. (Glossary of basic terms in polymer science (IUPAC Recommendations 1996)) on page 2291 [Terms] [Paper]