643
643 is a prime, odd, a calendar year.
643 (six hundred forty-three) is an odd 3-digit number. It is a prime number — divisible only by 1 and itself. Written other ways, in Roman numerals it is DCXLIII and in binary, 1010000011.
Interestingness
Historical context — 643 AD
Calendar year
Year 643 (DCXLIII) was a common year starting on Wednesday of the Julian calendar.
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Historical context — 643 BC
Calendar year
The year 643 BC was a year of the pre-Julian Roman calendar.
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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
-
Sunday
January 1, 643
- Ended on
-
Sunday
December 31, 643
- Friday the 13ths
-
2
2 Friday the 13ths this year.
- Decade
-
640s
640–649
- Century
-
7th century
601–700
- Millennium
-
1st millennium
1–1000
- Years ago
-
1,383
1383 years before 2026.
In other calendars
- Hebrew
-
4403 / 4404 AM
Rosh Hashanah falls in September/October.
- Islamic Hijri
-
22 / 23 AH
Lunar calendar; year spans differ from Gregorian.
- Chinese
-
Year of the zodiac:Water zodiac:Rabbit
Sexagenary cycle position 40 of 60. Lunar new year falls in late January / mid-February.
- Buddhist Era
-
1186 BE
Counted from the parinirvana of the Buddha (Theravada / Thai / Sri Lankan convention).
- Persian Solar Hijri
-
21 / 22 SH
Iranian calendar; Nowruz (new year) falls on the spring equinox.
- Ethiopian
-
635 / 636 ET
Year boundary at Enkutatash (September 11/12).
- Indian National (Saka)
-
565 / 564 Saka
Indian national calendar; year starts in March.
Properties
Primality
643 is prime. It has exactly two divisors: 1 and itself.
Divisors & multiples
Sums & aliquot sequence
Continued fraction of √n
√643 = [25; (2, 1, 3, 1, 16, 8, 2, 1, 1, 5, 25, 5, 1, 1, 2, 8, 16, 1, 3, 1, 2, 50)]
Period length 22 — the block in parentheses repeats forever.
Representations
- In words
- six hundred forty-three
- Ordinal
- 643rd
- Roman numeral
- DCXLIII
- Binary
- 1010000011
- Octal
- 1203
- Hexadecimal
- 0x283
- Base64
- AoM=
- One's complement
- 64,892 (16-bit)
- Scientific notation
- 6.43 × 10²
- As a duration
- 643 s = 10 minutes, 43 seconds
As an angle
Historical numeral systems
- Babylonian (base 60)
- 𒌋 𒌋𒌋𒌋𒌋𒁹𒁹𒁹
- Egyptian hieroglyphic
- 𓍢𓍢𓍢𓍢𓍢𓍢𓎆𓎆𓎆𓎆𓏺𓏺𓏺
- Greek (Milesian)
- χμγʹ
- Mayan (base 20)
- 𝋡·𝋬·𝋣
- Chinese
- 六百四十三
- Chinese (financial)
- 陸佰肆拾參
Digit at this position in famous constants
- π — Pi (π)
- Digit 643 = 3
- e — Euler's number (e)
- Digit 643 = 6
- φ — Golden ratio (φ)
- Digit 643 = 6
- √2 — Pythagoras's (√2)
- Digit 643 = 4
- ln 2 — Natural log of 2
- Digit 643 = 8
- γ — Euler-Mascheroni (γ)
- Digit 643 = 4
Also seen as
UTF-8 encoding: CA 83 (2 bytes).
As an unsigned 32-bit integer, this is the IPv4 address 0.0.2.131.
- Address
- 0.0.2.131
- Class
- reserved
- IPv4-mapped IPv6
- ::ffff:0.0.2.131
Unspecified address (0.0.0.0/8) — "this network" placeholder.
Heard as a frequency, 643 Hz is closest to:
- Concert pitch (A4 = 440 Hz): E5 (659.3 Hz, -43¢)
- Scientific pitch (C4 = 256 Hz): E5 (645.1 Hz, -6¢)
- Baroque pitch (A4 = 415 Hz): F5 (658.8 Hz, -42¢)
Related reading
- Prime numbers — The building blocks of arithmetic: what primes are, why they matter, and how we find them.
- Egyptian hieroglyphic numerals — Seven hieroglyphs for every power of ten, from a single stroke to a million.