Five
Five (5) is the natural number following four and preceding six.Five is the third smallest prime number, the next is seven. Because it can be written as 2^(2^1)+1, five is classified as a Fermat prime.
Five is a factor of 10, so fractions with 5 in the denominator do not yield infinite decimal expansions, unlike most other primes.
While polynomial equations of degree 4 and below can be solved with radicals, equations of degree 5 and higher cannot generally be so solved. This is the Abel-Ruffini theorem. This is related to the fact that the symmetric group Sn is a solvable group for n ≤ 4 and not solvable for n ≥ 5.
While all graphs with 4 or fewer vertices are planar, there exists a graph with 5 vertices which is not planar: K5, the complete graph with 5 vertices.
The Roman numeral for five is V.
In Cantonese, five sounds like the word "not" (symbol 唔). So when five appears in front of a lucky number, e.g. 58, the result is considered unlucky.
Giving five refers to slapping hands with someone as a sign of approbation.
Five is also:
- the number of sides in a pentagon
- the number of Platonic solids.
- the number of dots in a quincunx
- the number of musicians in a quintet.
- the number of permanent members with veto power on the UN Security Council.
- almost all amphibians, reptiles, birds and mammals which have fingers or toes have five of them on each extremity.
- The Garden of Cyrus A Pythagorean Discourse based upon the number 5
See also: three, four, five, six, seven, integer, list of numbers.
This article is about the number. For the year 5 AD, see 5.
For the UK TV channel Five, see Five (TV).
