Английская Википедия:280 (number)
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Шаблон:Hatnote Шаблон:Refimprove Шаблон:Infobox 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). Шаблон:Disputed-inline
Integers from 281 to 289
281
282
283
284
285
286
287
288
289
References
Шаблон:Reflist Шаблон:Integers
