280 (number)

This article covers the number 280. For the year, see 280.

280 (two hundred [and] eighty) is the natural number after 279 and before 281.

← 279 280 281 →
← 200 210 220 230 240 250 260 270 280 290 → List of numbers Integers ← 0 100 200 300 400 500 600 700 800 900 →
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

In mathematics

The denominator of the eighth harmonic number, 280 is an octagonal number. 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).

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)