75 (number)

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

In mathematics
75 is a self number because there is no integer that added up to its own digits adds up to 75. It is the sum of the first five pentagonal numbers, and therefore a pentagonal pyramidal number, as well as a nonagonal number.

It is also the fourth ordered Bell number, and a Keith number, because it recurs in a Fibonacci-like sequence started from its base 10 digits: 7, 5, 12, 17, 29, 46, 75...

75 is the count of the number of weak orderings on a set of four items.

Excluding the infinite sets, there are 75 uniform polyhedra in the third dimension, which incorporate star polyhedra as well. Inclusive of 7 families of prisms and antiprisms, there are also 75 uniform compound polyhedra.

In other fields
Seventy-five is:


 * The atomic number of rhenium
 * The age limit for Canadian senators
 * 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