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

Шаблон:Main

282

Шаблон:Main

283

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284

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285

Шаблон:Main

286

Шаблон:Main

287

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288

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289

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References

Шаблон:Reflist Шаблон:Integers