Open your hands and turn down the Nth finger. 9•N is the the number of fingers to the left of it in the 10s position and the number of fingers to the right in the unit position.
I use 5, 8, 11, 17 and 35 times table daily. I would say it’s best to practice repetition if you want to remember something. Plus your teachers lied to you, you will always have a calculator with you!