Forty

The forty (40) is the natural number that follows 39 and precedes 41.

Math

• It is a composite number that has the following factors: 1, 2, 4, 5, 8, 10 and 20. As the sum of its own dividers is 50  40 is an abundant number. The sum of its dividers 1, 2, 4, 5, 8, 10, 20 and 40 = 90
• It's a semi-perfect number.
• It's an octogonal number.
• Forty is the number of solutions to the problem of the eight queens for n = 7.
• It's a Harshad number.

Chemistry

• It is the atomic number of zirconium (Zr).

Astronomy.

• Astronomical object of the New General Catalog: NGC 40 is a reddish planetary nebula in the constellation of Cepheus.