280 (number)

Last updated
279 280 281
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

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 ]

Related Research Articles

33 (thirty-three) is the natural number following 32 and preceding 34.

29 (twenty-nine) is the natural number following 28 and preceding 30. It is a prime number.

28 (twenty-eight) is the natural number following 27 and preceding 29.

65 (sixty-five) is the natural number following 64 and preceding 66.

96 (ninety-six) is the natural number following 95 and preceding 97. It is a number that appears the same when turned upside down.

113 is the natural number following 112 and preceding 114.

1000 or one thousand is the natural number following 999 and preceding 1001. In most English-speaking countries, it can be written with or without a comma or sometimes a period separating the thousands digit: 1,000.

700 is the natural number following 699 and preceding 701.

600 is the natural number following 599 and preceding 601.

800 is the natural number following 799 and preceding 801.

2000 is a natural number following 1999 and preceding 2001.

3000 is the natural number following 2999 and preceding 3001. It is the smallest number requiring thirteen letters in English.

5000 is the natural number following 4999 and preceding 5001. Five thousand is, at the same time, the largest isogrammic numeral, and the smallest number that contains every one of the five vowels in the English language.

6000 is the natural number following 5999 and preceding 6001.

8000 is the natural number following 7999 and preceding 8001.

100,000 (one hundred thousand) is the natural number following 99,999 and preceding 100,001. In scientific notation, it is written as 105.

225 is the natural number following 224 and preceding 226.

20,000 is the natural number that comes after 19,999 and before 20,001.

30,000 is the natural number that comes after 29,999 and before 30,001.

50,000 is the natural number that comes after 49,999 and before 50,001.

References

  1. "Sloane's A002805 : Denominators of harmonic numbers". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. Retrieved 2016-05-28.
  2. "Sloane's A000567 : Octagonal numbers". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. Retrieved 2016-05-28.