Depositing information and structures related to location of receptor binding sites in various HA structures
You can consult the link below for informatin regarding the numbering system of residues of influenza virus http://www.antigenic-cartography.org/surveillance/evergreen/HAnumbering/
Note however that not all PDBs have number their residues consistent with this numbering. It is possible to see for instance H5 structures which are numbered like H3 structures.