42
42 is a composite number, even, a calendar year.
In Douglas Adams' The Hitchhiker's Guide to the Galaxy, 42 is the answer computed by the supercomputer Deep Thought to the Ultimate Question of Life, the Universe, and Everything.
Mathematically, 42 is a sphenic number (the product of three distinct primes: 2 × 3 × 7), a pronic number, an abundant number, and the third primary pseudoperfect number. In 2019, mathematicians at the University of Bristol and MIT found a representation of 42 as a sum of three cubes:
\(42 = (-80\,538\,738\,812\,075\,974)^3 + 80\,435\,758\,145\,817\,515^3 + 12\,602\,123\,297\,335\,631^3\)
It was the last number under 100 for which such a representation was unknown.
Historical context — 42 AD
Calendar year
AD 42 (XLII) was a common year starting on Monday of the Julian calendar.
Excerpt from Wikipedia (en) ↗ · Licensed CC BY-SA 4.0 · English fallback Read the full article on Wikipedia →
Notable events — 42 BC
- Oct 23 Octavian and Antony defeat Brutus and Cassius at Philippi.
Events compiled from Wikipedia ↗ · Licensed CC BY-SA 4.0
Year facts
- Year type
-
Common year
Standard 365-day year; not divisible by 4 (or divisible by 100 but not 400).
- Days in year
- 365
- ISO weeks
- 52
- Started on
-
Wednesday
January 1, 42
- Ended on
-
Wednesday
December 31, 42
- Friday the 13ths
-
1
One Friday the 13th this year.
- Decade
-
40s
40–49
- Century
-
1st century
1–100
- Millennium
-
1st millennium
1–1000
- Years ago
-
1,984
1984 years before 2026.
In other calendars
- Hebrew
-
3802 / 3803 AM
Rosh Hashanah falls in September/October.
- Chinese
-
Year of the zodiac:Water zodiac:Tiger
Sexagenary cycle position 39 of 60. Lunar new year falls in late January / mid-February.
- Buddhist Era
-
585 BE
Counted from the parinirvana of the Buddha (Theravada / Thai / Sri Lankan convention).
- Ethiopian
-
34 / 35 ET
Year boundary at Enkutatash (September 11/12).
- Indian National (Saka)
-
-36 / -37 Saka
Indian national calendar; year starts in March.
Cultural significance
The Answer to the Ultimate Question of Life, the Universe, and Everything.
Douglas Adams, The Hitchhiker's Guide to the Galaxy.
Sourced from Wikipedia (Numerology, Chinese numerology, Gematria, and per-culture articles).
Properties
Primality
Prime factorization: 2 × 3 × 7
Divisors & multiples
Sums & aliquot sequence
Continued fraction of √n
√42 = [6; (2, 12)]
Period length 2 — the block in parentheses repeats forever.
Representations
- In words
- forty-two
- Ordinal
- 42nd
- Roman numeral
- XLII
- Binary
- 101010
- Octal
- 52
- Hexadecimal
- 0x2A
- Base64
- Kg==
- One's complement
- 213 (8-bit)
- Scientific notation
- 4.2 × 10¹
Historical numeral systems
- Babylonian (base 60)
- 𒌋𒌋𒌋𒌋𒁹𒁹
- Egyptian hieroglyphic
- 𓎆𓎆𓎆𓎆𓏺𓏺
- Greek (Milesian)
- μβʹ
- Mayan (base 20)
- 𝋢·𝋢
- Chinese
- 四十二
- Chinese (financial)
- 肆拾貳
Digit at this position in famous constants
- π — Pi (π)
- Digit 42 = 6
- e — Euler's number (e)
- Digit 42 = 4
- φ — Golden ratio (φ)
- Digit 42 = 0
- √2 — Pythagoras's (√2)
- Digit 42 = 7
- ln 2 — Natural log of 2
- Digit 42 = 0
- γ — Euler-Mascheroni (γ)
- Digit 42 = 5
Also seen as
Goldbach's conjecture says every even integer greater than 2 is the sum of two primes. For 42, here are decompositions:
- 5 + 37 = 42
- 11 + 31 = 42
- 13 + 29 = 42
- 19 + 23 = 42
As an ASCII codepoint, 42 is *. Printable ASCII character *.
As an unsigned 32-bit integer, this is the IPv4 address 0.0.0.42.
- Address
- 0.0.0.42
- Class
- reserved
- IPv4-mapped IPv6
- ::ffff:0.0.0.42
Unspecified address (0.0.0.0/8) — "this network" placeholder.
This passes the ABA routing number checksum and matches the Federal Reserve numbering scheme.
Banks operate many routing numbers per state and division; an unmatched checksum-valid number can still be a real RTN at a smaller institution.
Heard as a frequency, 42 Hz is closest to:
- Concert pitch (A4 = 440 Hz): E1 (+33¢)
- Scientific pitch (C4 = 256 Hz): F1 (-29¢)
On the periodic table, atomic number 42 is Molybdenum (Mo) — period 5.