231 (number)

Template:Infobox number 231 (two hundred [and] thirty-one) is the natural number following 230 and preceding 232.

In Mathematics

• 231 is a sphenic number.
• 231 is the 21st triangular number, a doubly triangular number, a hexagonal number, an octahedral number and a centered octahedral number.
• 231 is palindromic in base 2 (11100111₂).
• There are 231 integer partitions of 16.
• 231 is a zero of Mertens function.

In measurement

A US gallon is defined by being exactly 231 cubic inches, the volume of a cylinder 7 inches in diameter and 6 inches tall, where $\pi$ is approximated as $\frac{22}{7}$.