What did Avogadro count the number of?
Avogadro didn’t count the number of anything.
In 1811, Avogadro proposed that equal volumes of gases at the same conditions of temperature and pressure contain equal numbers of molecules.
It wasn’t until 1827 that Robert Brown made the first crude measurement of the number of molecules in a mole.
And it wasn’t until 1909 that the French physicist Jean Perrin proposed naming that number in honour of Avogadro.