Part 3 · Rudiments · Chapter 39
The seven-stroke roll is three doubles and an accent: R R L L R R L. It is a longer version of the five-stroke roll and, because of the odd number of doubles, it ends on the opposite hand.
The roll fills three sixteenths and lands on the a.
Three doubles and a single, at half speed.
Five-stroke: two doubles. Seven-stroke: three. Nine-stroke: four. The number in the name is always the doubles times two, plus one.