42 (number)
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42 is a natural number used for counting, positioned between 41 and 43. In the standard base-ten system it is written with two digits: 4 and 2. It is an even number, as it is divisible by two with no remainder.
42 is not a prime number, as it has divisors other than 1 and itself. Its divisors are 1, 2, 3, 6, 7, 14, 21, and 42. Its prime factorization is 2 × 3 × 7, making it the product of three distinct prime numbers.
Mathematical properties
The sum of the divisors of 42 that are less than itself is 1 + 2 + 3 + 6 + 7 + 14 + 21 = 54, which exceeds 42. For this reason 42 is classified as an abundant number. Additionally, 42 equals the sum of the first six even numbers: 2 + 4 + 6 + 8 + 10 + 12 = 42.
In other number systems, 42 can be written as 101010 in binary (base two) and as 2A in hexadecimal (base sixteen). The binary representation 101010 is often cited in computing literature.
Uses and significance
42 appears in many contexts: it is the number of months in three years, and the number of pips on a standard double-six domino set when all pips are counted. It is also used practically as a number designation for roads, districts, and games.
In contemporary English-language culture, 42 is recalled from the science fiction novel The Hitchhiker's Guide to the Galaxy by Douglas Adams, where the number is presented as the answer to "the ultimate question of life, the universe, and everything." This is a literary reference rather than a mathematical property, but it has led to 42 being regularly discussed in media and on the internet.