The number of students admitted from the wait-Iist each year is different. However I have figured out last year’s number as follows:
(1) From (http://www.browndailyherald.com/2017/03/30/u-admits-record-low-8-3-percent-applicants-class-2021/), 2027 RD + 695 ED were admitted. The total is 2722.
(2) From (https://news.brown.edu/articles/2017/09/firstyear), The University admitted 2,801 students, yielding a matriculating class of 1,643.
So 79 (2801-2722) candidates were later admitted from wait-list last year.