Table schema:
CREATE TABLE table_name_65 (number_of_seasons_in_top_division INTEGER, number_of_seasons_in_prva_hnl VARCHAR)

Question: Name the average number of seasons for Prva HNL of 17
SQL: SELECT AVG(number_of_seasons_in_top_division) FROM table_name_65 WHERE number_of_seasons_in_prva_hnl = 17