Fatto generale: 30 is the number of uprights that formed the Sarsen Circle at Stonehenge, also the supposed number of holes forming the arrays of Y and Z Holes at Stonehenge.
Fatto matematico: 30 is the largest number with the property that all smaller numbers relatively prime to it are prime.
Trivia: 30 is the duration in years of the Thirty Years' War - 1618 to 1648.
Data storica: January 30th is the day in 1960 that the African National Party is founded in Chad, through the merger of traditionalist parties.