\[= \left( a^{24} - 1 \right)\left( a^{24} + 1 \right)\left( a^{48} + 1 \right) =\]
\[= \left( a^{48} - 1 \right)\left( a^{48} + 1 \right) =\]
\[= \left( a^{96} - 1 \right)\]