Hecho matemático: 8521 is a prime that is the average of two 4^{th} powers.
Trivia: 8521 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Fecha histórica: April 30th is the day in 1999 that Cambodia joins the Association of Southeast Asian Nations (ASEAN) bringing the number of members to 10.