Unknown piano thu/tru something?

Hi. My piano teacher wrote down my homework and for the life of me I can't read his writing.He mentioned something along the lines of the c scale and then said i should do (idk) thueision, truesions thueisions trueisions i can't read the writing but thats what i tried and got when I deciphered it. We did it together and its like going up the keyes whith three finger chords and it changes every time then your back to the same notes. The he gave was 531 521 531 531 and it moves up every time. Does anyone have any idea? I dont know ill give more info l8er gtg