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This article covers the number 280. For the year, see 280.
Natural number
280 (two hundred [and] eighty) is the natural number after 279 and before 281.
In mathematics
The denominator of the eighth harmonic number,[1] 280 is an octagonal number.[2] 280 is the smallest octagonal number that is a half of another 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). [disputed – discuss]
Integers from 281 to 289
281
Main article: 281 (number)
282
Main article: 282 (number)
283
Main article: 283 (number)
284
Main article: 284 (number)
285
Main article: 285 (number)
286
Main article: 286 (number)
287
Main article: 287 (number)
288
Main article: 288 (number)
289
Main article: 289 (number)
References
- ^ "Sloane's A002805 : Denominators of harmonic numbers". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. Retrieved 2016-05-28.
- ^ "Sloane's A000567 : Octagonal numbers". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. Retrieved 2016-05-28.
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