Solution 34592: Calculating Logs of Bases Other Than 10 Using the TI-84 Plus C Silver Edition.
How do I calculate logs of bases other than 10 using a TI-84 Plus C Silver Handheld?The logbase( function can be used to perform log calculations with bases other than 10 using the TI-84 Plus C Silver Edition.
Example: Calculate log4 160
• Press [ALPHA] [F2]  to access the FUNC menu and insert the logbase( function.
• Input 4 for the base.
• Scroll to the right and input 160 for the log value.
• Press [ENTER] to complete the calculation.
Please see the TI-84 Plus C Silver Edition guidebook for additional information.