## Wikipedia - Avogadro constant Avogadro constant, $$N_{\text{A}}$$, $$L$$

https://doi.org/10.1351/goldbook.A00543
The Avogadro constant, $$N_{\text{A}} = 6.022\ 140\ 76 \times 10^{23}\ \text{mol}^{-1}$$, is a proportionality constant between the quantity @A00297@ ($$n$$, with unit mole) and the quantity for counting @N04266@ ($$N$$ with unit one, symbol 1), $$N = N_{\text{A}}\ n$$.
Notes:
1. In the revision of the International System of Units (SI) of 2019 the Avogadro constant became one of the seven defining constants with the exact value $$6.022\ 140\ 76 \times 10^{23}\ \text{mol}^{-1}$$.
2. The Avogadro number is the exact numerical value of the Avogadro constant, $$6.022\ 140\ 76 \times 10^{23}$$
3. While the symbol $$N_{\text{A}}$$ is used to honour Amedeo Avogadro, the symbol $$L$$ is used in honour of Josef Loschmidt.
Sources:
BIPM, Le Système international d’unités (SI), SI Brochure, 9e ed. (2019) [Terms] [Book]
BIPM, The International System of Units, SI Brochure, 9th ed. (2019) [Terms] [Book]
Green Book, 3rd ed. [Terms] [Book]