40 is the natural number following 39 and preceding 41. In English, forty is the only number whose constituent letters appear in alphabetical order.
In mathematics
Forty is an octagonal number, and as the sum of the first four pentagonal numbers, it is a pentagonal pyramidal number. It is a Harshad number.
Given 40, the Mertens function returns 0. 40 is the smallest number n with exactly 9 solutions to the equation φ(x) = n.
Forty is the number of n-queens problem solutions for n = 7.
In astronomy
In other fields
Forty is also:
- The atomic number of zirconium
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Negative forty is the temperature at which the Fahrenheit and Celsius scales correspond; that is, -40°F = -40°C. It is referred to as either "minus forty" or "forty below".
- in Judaic, Christian and Islamic tradition: the tag Forty days and forty nights describes the period for which rain fell during Noah's flood, the period Moses spent on Mount Sinai receiving the Ten Commandments and the period Christ spent in the wilderness. In modern Western Christian practice, Lent consists of the 40 days preceding Easter
- the usual number of days in the time of mourning in Muslim cultures.
- the number of days after death for which the ghosts of the dead hang around the site of their death, according to Russian belief
- in the maxim "Life begins at forty".
- in the expression "Forty winks ", meaning a short sleep.
- the number of years of marriage as the ruby wedding anniversary.
- the code for direct dial international phone calls to Romania.
- the number in the designation of:
- the title of a song by U2.
- in the title of the Food Network show $40 a Day.
- in the name of WD-40, a type of spray lubricant.
- in the name of the food additive FD & C Red Dye #40, commonly known as "Red 40" [1]
- the 40 ounce size used for liquor, typically fairly cheap malt beer
- number of thieves in Ali Baba and the Forty Thieves from Thousand and One Nights - both numbers (40 and 1001) are more likely to mean "many" than to indicate a specific number
- the number of hours in a regular work week
- the year A.D. 40, 40 BC, or (for example) 1940.
Last updated: 05-21-2005 22:54:10
Last updated: 08-26-2005 14:41:28