It is wasteful to power individual 1.7V LEDs from a 9V battery because 7V is not used for the LEDs. Connect 2 LEDs in series and in series with a 220 ohm resistor for 25.5mA with a new 9V battery and 11.8mA when the battery voltage has dropped to 6V. Make 5 groups like this.

The LEDs probably have a "typical" voltage of 1.7V but it could be 2V max. Then 3 in series wouldn't light when the battery voltage drops to 6V and they would be very dim for most of the time.

Originally Posted by Richard Principal

you dont need any resistor if you put say 10 1.7 Volt LED in series and run it off 17 Volts you would not have to limit the current.

The voltage rating for the LEDs "might" be 1.7V, but it isn't guaranteed. They might actually be 1.6V then without a current-limiting resistor their current would be way too high and they will blow up. They could actually be 1.8V or even 2.0V then they won't light unless some extra voltage is provided.

He doesn't have 17V. He is thinking of using two 9V batteries, that produce about 19V when new and drop to 12V when finished.