Fatto matematico: 1551 is the number of trees on 25 vertices with diameter 4.
Trivia: 1551 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Data storica: March 30th is the day in 1885 that the Battle for Kushka triggers the Panjdeh Incident which nearly gives rise to war between the British Empire and Russian Empire.