42
42 is a composite number, famous as the fictional 'Answer to the Ultimate Question of Life, the Universe, and Everything' from The Hitchhiker's Guide to the Galaxy.
- Even
- Composite
Where 42 fits
Why 42 is special
42's cultural fame from Douglas Adams' novel gives it a media significance entirely disconnected from its fairly ordinary mathematical profile.
See 42 visually
Prime factorisation
42 = 2 × 3 × 7
These three primes are the building blocks of 42 — multiplying them together gives 42, and there's no other way to build 42 from primes.
42 is part of
Factors & digit properties
- Divisors (8)
- 1, 2, 3, 6, 7, 14, 21, 42
- Prime factorisation
- 2 × 3 × 7
- Digit sum
- 6
- Digital root
- 6
Representations
- Decimal
- 42
- Binary
- 101010
- Octal
- 52
- Hexadecimal
- 2a
- Roman numeral
- XLII
- Scientific notation
- 4.200 × 10^1
Other mathematical patterns
- Abundant number
- Harshad (Niven) number
Related numbers & connections
7 divides 42 evenly (42 = 7 × 6).
View 7 →42 is the fictional 'Answer to the Ultimate Question' in The Hitchhiker's Guide to the Galaxy.
Media & popular culture
42 is the fictional 'Answer to the Ultimate Question of Life, the Universe, and Everything' computed by the supercomputer Deep Thought in Douglas Adams' The Hitchhiker's Guide to the Galaxy (1979), and has since become a recurring cultural in-joke referencing the novel.
DocumentedMedia & popular culture
Common questions
Why is 42 famous?
It's the fictional 'Answer to the Ultimate Question of Life, the Universe, and Everything' from Douglas Adams' The Hitchhiker's Guide to the Galaxy — a joke about how an unsatisfying, ordinary-looking number could be presented as a profound cosmic answer.
Why is 42 used in computing and internet jokes?
Mainly because of the Hitchhiker's Guide reference itself — the book became widely read in early hacker and programmer culture, and 42 was adopted as a recurring in-joke (for example, as a placeholder or 'magic number' in code) referencing the novel rather than any property of the number itself.
Did Douglas Adams intend a hidden meaning behind 42?
He said the opposite — in later interviews and writing, Adams was consistent that he picked 42 as a deliberately mundane, ordinary number, and explicitly rejected fan theories looking for a hidden mathematical or numerological explanation.
Is 42 a prime number?
No, 42 is not prime.
What are the factors of 42?
The factors of 42 are 1, 2, 3, 6, 7, 14, 21, 42.
What is 42 in Roman numerals?
42 in Roman numerals is XLII.
About this page's data
Mathematical facts:computed directly from the number's value — nothing to source or verify externally.
Contextual records: 1 reviewer-confirmed record, sourced and reviewed before publication.
Last reviewed: 15 July 2026