First problem you have is that any color other than red LEDs need more than 1.6V each. You should check the data sheet. If you haven't got access to the data sheet tell us the color and how old the LED is and someone will guess. Also, your LEDs might be best at a current other than 18mA.
Second, when choosing a series resistor for LEDs you can easily go +/- 10%; more if you're not trying to match brightness. You could use 560, 620, or 680 ohms if brightness isn't critical.
When the motor is running the voltage will be close to 14V so re-do the calculations for that.