In Mathematics
The denominator of the eighth harmonic number, 280 is an octagonal number.
There are 280 plane trees with ten nodes. As a consequence of this, 18 people around a round table can shake hands with each other in non-crossing ways, in 280 different ways (this includes rotations).
280 is a base 10 Harshad number.
Read more about this topic: 280 (number)
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