72 (number)


72 is the natural number following 71 and preceding 73. It is half a gross or 6 dozen.

In mathematics

Seventy-two is the sum of four consecutive primes, as well as the sum of six consecutive primes. The product of 8 and 9, 72 is a pronic number. The sum of Euler's totient function φ over the first fifteen integers is 72. There are 17 solutions to the equation φ = 72, more than any integer below 72, making it a highly totient number.
72 is the smallest number whose fifth power is the sum of five smaller fifth powers: 195 + 435 + 465 + 475 + 675 = 725.
The sum of the eighth row of Lozanić's triangle is 72.
In a plane, the exterior angles of a regular pentagon measure 72 degrees each.
In base 10, the number 72 is a Harshad number.
In maths and economics, 72 plays a role in the Rule of 72.

In science

Seventy-two is also: