Provide the number of students at Yale University in 2016.
number of students refers to num_students; Yale University refers to university_name = 'Yale University'; in 2016 refers to year = 2016
SELECT T1.num_students FROM university_year AS T1 INNER JOIN university AS T2 ON T1.university_id = T2.id WHERE T2.university_name = 'Yale University' AND T1.year = 2016