Fatto matematico: 8506 is the number of isomers of C_{13}H_{26} without any double bonds.
Trivia: 8506 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Data storica: April 15th is the day in 1802 that William Wordsworth and his sister, Dorothy see a "long belt" of daffodils, inspiring the former to pen I Wandered Lonely as a Cloud.