General fact: 526 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Mathematical fact: 526 is the number of ways to cut a 8×8 chessboard into 2 pieces with equal areas with a cut that only travels up and right.
Trivia: 526 is an uninteresting number.
Historical date: June 9th is the day in 1978 that the Church of Jesus Christ of Latter-day Saints opens its priesthood to "all worthy men", ending a 148-year-old policy excluding black men.