Fatto generale: 156 is the number of years that Hong Kong was under British colony rule.
Fatto matematico: 156 is the number of graphs with 6 vertices.
Trivia: 156 is the number of strikes a clock will strike in the course of a day.
Data storica: June 4th is the day in 1920 that Hungary loses 71% of its territory and 63% of its population when the Treaty of Trianon is signed in Paris.