\[\frac{a^{23} \cdot (b^5)^4}{(a \cdot b)^{20}} = \frac{a^{23} \cdot b^{5 \cdot 4}}{a^{20} \cdot b^{20}} = \frac{a^{23} \cdot b^{20}}{a^{20} \cdot b^{20}}\]
\[\frac{a^{23}}{a^{20}} \cdot \frac{b^{20}}{b^{20}} = a^{23-20} \cdot b^{20-20} = a^3 \cdot b^0 = a^3 \cdot 1 = a^3\]
\[a^3 = 2^3 = 8\]
Ответ: 8.