231 (two hundred [and] thirty-one) is the natural number following 230 and preceding 232.
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). 231 is the number of integer partitions of 16. The Mertens function of 231 returns 0.
In other fields 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 π {\displaystyle \pi } is approximated as 22 7 {\displaystyle {\frac {22}{7}}} .
Religion 231 in the Kabbalistic text Sefer Yetzirah is identified as the number of “gates” in the Hebrew alphabet, mystical combinations of two unique letters where order is interchangeable.
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