280 (number)

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

Short description: Natural number

← 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
Quaternary	101204
Quinary	21105
Senary	11446
Octal	4308
Duodecimal	1B412
Hexadecimal	11816
Vigesimal	E020
Base 36	7S36

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

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).