## The first Zagreb index 30 years after.(English)Zbl 1053.05115

The sum of the squares of vertex degrees of a graph is called the first Zagreb index in chemical literature after it was used more than 30 years ago by the first author and N. Trinajstić (both located in Zagreb at the time) in a paper [Chem. Phys. Lett. 17, 535–538 (1972)] on the total $$\pi$$-electron energy of a molecule. The present paper is a complement of a similar survey on Zagreb indices written by Nikolić, Kovačević, Milićević and Trinajstić [Croat. Chem. Acta 76, 113–124 (2003)]

### MSC:

 05C90 Applications of graph theory

### Keywords:

vertex degree; first Zagreb index