280 (number)

From HandWiki
This article covers the number 280. For the year, see 280.
Short description: Natural number
← 279 280 281 →
Cardinaltwo hundred eighty
Ordinal280th
(two hundred eightieth)
Factorization23 × 5 × 7
Greek numeralΣΠ´
Roman numeralCCLXXX
Binary1000110002
Ternary1011013
Quaternary101204
Quinary21105
Senary11446
Octal4308
Duodecimal1B412
Hexadecimal11816
VigesimalE020
Base 367S36

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

  1. ↑ "Sloane's A002805 : Denominators of harmonic numbers". OEIS Foundation. https://oeis.org/A002805. 
  2. ↑ "Sloane's A000567 : Octagonal numbers". OEIS Foundation. https://oeis.org/A000567. 



Retrieved from "https://handwiki.org/wiki/index.php?title=280_(number)&oldid=298044"