# All Science Fair Projects

## Science Fair Project Encyclopedia for Schools!

 Search    Browse    Forum  Coach    Links    Editor    Help    Tell-a-Friend    Encyclopedia    Dictionary

# Science Fair Project Encyclopedia

For information on any area of science that interests you,
enter a keyword (eg. scientific method, molecule, cloud, carbohydrate etc.).
Or else, you can start by choosing any of the categories below.

# 40 (number)

(Redirected from Forty)

40 is the natural number following 39 and preceding 41. In English, forty is the only number whose constituent letters appear in alphabetical order.

 Cardinal forty Ordinal 40th (fortieth) Numeral system Factorization $2^3 \cdot 5$ Divisors 2, 4, 5, 8, 10, 20 Roman numeral XL Binary 101000 Hexadecimal 28 Hebrew מ (Mem)

## 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 other fields

Forty is also:

03-10-2013 05:06:04