Randić's molecular connectivity index

The Randić index, also known as the connectivity index, of a graph is the sum of bond contributions ${\displaystyle 1/(d_{i}d_{j})^{1/2}}$where ${\displaystyle d_{i}}$and ${\displaystyle d_{j}}$are the degrees of the vertices making bond i ~ j.

This graph invariant was introduced by Milan Randić in 1975. It is often used in chemoinformatics for investigations of organic compounds.

• Roberto Todeschini, Viviana Consonni (2009) "Molecular Descriptors for Chemoinformatics", Wiley-VCH,ISBN 978-3-527-31852-0
• Li, Xueliang; Shi, Yongtang (2008), "A survey on the Randić index", MATCH Communications in Mathematical and in Computer Chemistry, 59 (1): 127–156.