280 (number): Difference between revisions
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==In mathematics== |
==In mathematics== |
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The denominator of the eighth [[harmonic number]],<ref>{{Cite web|url=https://oeis.org/A002805|title=Sloane's A002805 : Denominators of harmonic numbers|website=The On-Line Encyclopedia of Integer Sequences|publisher=OEIS Foundation|access-date=2016-05-28}}</ref> 280 is an [[octagonal number]].<ref>{{Cite web|url=https://oeis.org/A000567|title=Sloane's A000567 : Octagonal numbers|website=The On-Line Encyclopedia of Integer Sequences|publisher=OEIS Foundation|access-date=2016-05-28}}</ref> |
The denominator of the eighth [[harmonic number]],<ref>{{Cite web|url=https://oeis.org/A002805|title=Sloane's A002805 : Denominators of harmonic numbers|website=The On-Line Encyclopedia of Integer Sequences|publisher=OEIS Foundation|access-date=2016-05-28}}</ref> 280 is an [[octagonal number]].<ref>{{Cite web|url=https://oeis.org/A000567|title=Sloane's A000567 : Octagonal numbers|website=The On-Line Encyclopedia of Integer Sequences|publisher=OEIS Foundation|access-date=2016-05-28}}</ref> 280 is the smallest number divisible by every natural number from 1 to 10 except the ones divisible by 3. 280 is the smallest octagonal number that is a half of another octagonal number. |
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There are 280 plane [[tree (graph theory)|tree]]s with ten nodes. |
There are 280 plane [[tree (graph theory)|tree]]s with ten nodes. |
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Revision as of 15:06, 5 July 2024
 | This article needs additional citations for verification. (May 2016) |
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|---|---|---|---|---|
| Cardinal | two hundred eighty | |||
| Ordinal | 280th (two hundred eightieth) | |||
| Factorization | 23 × 5 × 7 | |||
| Greek numeral | ΣΠ´ | |||
| Roman numeral | CCLXXX | |||
| Binary | 1000110002 | |||
| Ternary | 1011013 | |||
| Senary | 11446 | |||
| Octal | 4308 | |||
| Duodecimal | 1B412 | |||
| Hexadecimal | 11816 | |||
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 number divisible by every natural number from 1 to 10 except the ones divisible by 3. 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
282
283
284
285
286
287
288
289
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.