Fatto generale: 1236 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Fatto matematico: 1236 is the number of conjugacy classes of the alternating group A_{26}.
Trivia: 1236 is an uninteresting number.
Data storica: May 20th is the day in 1497 that John Cabot sets sail from Bristol, England, on his ship Matthew looking for a route to the west (other documents give a May 2 date).