So this is sort of like Sudoku in reverse? :)
Reminds me of the time when I had a Nintendo DS -- well I still do, but it's in a deep slumber somewhere out there in the boxes of stuff -- I also had Brain Age to go with it. And sure brain training apps have boomed since then, but that's where the trend really started... Where was I?
Math! Simple math, just quickly solving equations and math puzzles is good for your top meatbox! The time trial element is apparently an important part of it.
Clearly I'm not giving the grey matter quite enough exercise right now...
It belongs in the group of sudoku-type puzzles. But for sudokus the numerical value of the number is not important whereas for rullo the numerical value is the most important thing.
If you like doing raw calculations you can always try this https://arithmetic.zetamac.com/ :o)