75 (number)

75 (seventy-five) is the natural number following 74 and preceding 76.

In mathematics[]

75 is:

• the fourth ordered Bell number, and counts the number of weak orderings on a set of four items.^[1]
• the sum of the first five pentagonal numbers, and therefore a pentagonal pyramidal number.^[2]
• a nonagonal number.^[3]
• a Keith number, because it recurs in a Fibonacci-like sequence started from its base 10 digits: 7, 5, 12, 17, 29, 46, 75...^[4]
• a self number because there is no integer that added up to its own digits adds up to 75.^[5]

Excluding the infinite sets, there are 75 uniform polyhedra (or 76 if edges are allowed to coincide).

In other fields[]

Seventy-five is:

• The atomic number of rhenium
• The age limit for Canadian senators^[6]
• A common name for the Canon de 75 modèle 1897, a French World War I gun
• The department number of the city of Paris
• The number of balls in a standard game of Bingo in the United States

References[]