General fact: 261 is number of possible unfolded tesseract patterns.
Mathematical fact: 261 is the number of essentially different ways to dissect a 16-gon into 7 quadrilaterals.
Trivia: 261 is number of possible unfolded tesseract patterns.
Historical date: September 17th is the day in 1908 that the Wright Flyer flown by Orville Wright, with Lieutenant Thomas Selfridge as passenger, crashes killing Selfridge.