This is the 412th most frequent Polish word.
uczestników
"Participants."
'uczestników' is used in the genitive plural form, denoting the recipients of the rewards prepared, showing the genitive relationship.
Organizatorzy przygotowali nagrody dla uczestników konkursu.
The organizers prepared rewards for the participants of the competition.
The word 'uczestników' is in the genitive plural form, indicating the participants who are recorded or listed in 'na liście' (on the list).
Na liście uczestników zabrakło kilku osób.
Several people were missing from the list of participants.
Here, 'uczestników' is used in the genitive plural form, describing the participants of the course, indicating possession or association with the noun 'liczba' (number).