Assuming you have max 170Vdc in the divider's input you can place a 13k 3W and a 3k 1W. This will give about 32V max in the input of 7805 when it sinks no current and it will give about 7.5V when it sinks about 8,2mA. The current drawn from the source would be about 10,7mA which is 1,5W of power in the 13k resistor and about 0.35W (max) in the 3k resistor.
If you power your 7805 from a bench power supply and you determine that you don't need 8mA of current, you can increase the resistor's values accordingly.