# Randić's molecular connectivity index

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

## History

This graph invariant was introduced by Milan Randić in 1975.[1] It is often used in chemoinformatics for investigations of organic compounds.

## Notes

1. ^ Randić, M. (1975), "Characterization of molecular branching", Journal of the American Chemical Society 97 (23): 6609–6615, doi:10.1021/ja00856a001.