153 (one hundred [and] fifty-three) is a natural number and integer following 152 and preceding 154.

It is the sum of the first 17 integers, and also the sum of the first five positive factorials. It is the 17th triangular number.

The number 153 is associated with the geometric shape known as the Vesica piscis or Mandorla. Archimedes, in his Measurement of a Circle, referred to this ratio (153/265), as constituting the "measure of the fish", this ratio being an imperfect representation of ${\displaystyle 1/{\sqrt {3}}\approx 0.57735}$.

As a triangular number, 153 is the sum of the first 17 integers, and is also the sum of the first five positive factorials: ${\displaystyle 1!+2!+3!+4!+5!}$.

The number 153 is also a hexagonal number, and a truncated triangle number, meaning that 1, 15, and 153 are all triangle numbers.

The distinct prime factors of 153 add up to 20, and so do the ones of 154, hence the two form a Ruth-Aaron pair.

Since ${\displaystyle 153=1^{3}+5^{3}+3^{3}}$, it is a 3-narcissistic number, and it is also the smallest three-digit number which can be expressed as the sum of cubes of its digits. Only five other numbers can be expressed as the sum of the cubes of their digits: 0, 1, 370, 371 and 407. It is also a Friedman number, since 153 = 3 × 51.

The Biggs–Smith graph is a symmetric graph with 153 edges, all equivalent.