The first number.

In The Hithchiker's Guide to the Galaxy, 42 is 'the answer to life, the universe and everything.'

Trilogies come in threes.

San Fransisco 49ers are an American Football team.

Harpers Bizarre had a single titled '59th Street Bridge Song (Feelin' Groovy)'.

Blackjack is a game in which 21 is the target.

The Holt graph has 54 edges.

The Babylonian number system was base 60.

The number 58 was commonly associated with misfortune in many civilizations native to either Central America or Southern America. Due to their beliefs in the original 58 sins, the number came to symbolize curses and ill-luck.

The Muqatta'at or "disconnected letters"; also "mysterious letters") are combinations of between one and five Arabic letters figuring at the beginning of 29 out of the 114 surahs (chapters) of the Quran just after the basmala.

Johann Sebastian Bach's Well-Tempered Clavier is informally known as The Forty-Eight because it consists of a prelude and a fugue in each major and minor key, for a total of forty-eight pieces.

In a leap year there are 29 days in the month of February whereas there are normally only 28.