| ||||
---|---|---|---|---|
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
[edit]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
[edit]281
[edit]282
[edit]283
[edit]284
[edit]285
[edit]286
[edit]287
[edit]288
[edit]289
[edit]References
[edit]- ^ "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.