Icosahedral capsids with a triangulation number T=9 are composed of 12 pentameric and 80 hexameric capsomeres for a total of 540 capsid proteins.

Icosahedric triangulation number is calculated following Caspar and Klug system

**Physical principles in the construction of regular viruses**

D. L. Caspar, A. Klug

Cold Spring Harb. Symp. Quant. Biol. 1962; 27: 1?24