Hecho matemático: 1553 is the number of polygons formed by 9 points on a circle, if adjacent points can not be joined.
Trivia: 1553 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Fecha histórica: April 1st is the day in 1941 that a military coup in Iraq overthrows the regime of 'Abd al-Ilah and installs Rashid Ali as Prime Minister.