3. Calculate: $a \cdot a^{2} \cdot a^{3} \cdot \cdots \cdot a^{100}=$
3. $a^{5050}=$

Translate the text above into English, please keep the original text's line breaks and format, and output the translation result directly. 

However, since the provided text is already in a mathematical form which is universal and does not require translation, the output remains the same:

3. $a^{5050}=$