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 is approximated as .
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