280 (number)
Natural number
From Wikipedia, the free encyclopedia
280 (two hundred [and] eighty) is the natural number after 279 and before 281.
| ||||
|---|---|---|---|---|
| Cardinal | two hundred eighty | |||
| Ordinal | 280th (two hundred eightieth) | |||
| Factorization | 23 × 5 × 7 | |||
| Greek numeral | ΣΠ´ | |||
| Roman numeral | CCLXXX, cclxxx | |||
| Binary | 1000110002 | |||
| Ternary | 1011013 | |||
| Senary | 11446 | |||
| Octal | 4308 | |||
| Duodecimal | 1B412 | |||
| Hexadecimal | 11816 | |||
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]