491
491 is a prime, odd, a calendar year.
491 (four hundred ninety-one) 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 CDXCI and in binary, 111101011.
Interestingness
Historical context — 491 AD
Calendar year
Year 491 (CDXCI) was a common year starting on Tuesday of the Julian calendar.
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Historical context — 491 BC
Calendar year
Year 491 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
-
Monday
January 1, 491
- Ended on
-
Monday
December 31, 491
- Friday the 13ths
-
2
2 Friday the 13ths this year.
- Decade
-
490s
490–499
- Century
-
5th century
401–500
- Millennium
-
1st millennium
1–1000
- Years ago
-
1,535
1535 years before 2026.
In other calendars
- Hebrew
-
4251 / 4252 AM
Rosh Hashanah falls in September/October.
- Chinese
-
Year of the zodiac:Metal zodiac:Goat
Sexagenary cycle position 8 of 60. Lunar new year falls in late January / mid-February.
- Buddhist Era
-
1034 BE
Counted from the parinirvana of the Buddha (Theravada / Thai / Sri Lankan convention).
- Ethiopian
-
483 / 484 ET
Year boundary at Enkutatash (September 11/12).
- Indian National (Saka)
-
413 / 412 Saka
Indian national calendar; year starts in March.
Properties
Primality
491 is prime. It has exactly two divisors: 1 and itself.
Divisors & multiples
Sums & aliquot sequence
Continued fraction of √n
√491 = [22; (6, 3, 4, 8, 1, 1, 1, 2, 1, 1, 21, 1, 1, 2, 1, 1, 1, 8, 4, 3, 6, 44)]
Period length 22 — the block in parentheses repeats forever.
Representations
- In words
- four hundred ninety-one
- Ordinal
- 491st
- Roman numeral
- CDXCI
- Binary
- 111101011
- Octal
- 753
- Hexadecimal
- 0x1EB
- Base64
- Aes=
- One's complement
- 65,044 (16-bit)
- Scientific notation
- 4.91 × 10²
- As a duration
- 491 s = 8 minutes, 11 seconds
As an angle
Historical numeral systems
- Babylonian (base 60)
- 𒁹𒁹𒁹𒁹𒁹𒁹𒁹𒁹 𒌋𒁹
- Egyptian hieroglyphic
- 𓍢𓍢𓍢𓍢𓎆𓎆𓎆𓎆𓎆𓎆𓎆𓎆𓎆𓏺
- Greek (Milesian)
- υϟαʹ
- Mayan (base 20)
- 𝋡·𝋤·𝋫
- Chinese
- 四百九十一
- Chinese (financial)
- 肆佰玖拾壹
Digit at this position in famous constants
- π — Pi (π)
- Digit 491 = 1
- e — Euler's number (e)
- Digit 491 = 2
- φ — Golden ratio (φ)
- Digit 491 = 6
- √2 — Pythagoras's (√2)
- Digit 491 = 5
- ln 2 — Natural log of 2
- Digit 491 = 9
- γ — Euler-Mascheroni (γ)
- Digit 491 = 6
Also seen as
UTF-8 encoding: C7 AB (2 bytes).
As an unsigned 32-bit integer, this is the IPv4 address 0.0.1.235.
- Address
- 0.0.1.235
- Class
- reserved
- IPv4-mapped IPv6
- ::ffff:0.0.1.235
Unspecified address (0.0.0.0/8) — "this network" placeholder.
Heard as a frequency, 491 Hz is closest to:
- Concert pitch (A4 = 440 Hz): B4 (493.9 Hz, -10¢)
- Scientific pitch (C4 = 256 Hz): B4 (483.3 Hz, +27¢)
- Baroque pitch (A4 = 415 Hz): C5 (493.5 Hz, -9¢)
Related reading
- Prime numbers — The building blocks of arithmetic: what primes are, why they matter, and how we find them.
- Mayan numerals — Vigesimal dots-and-bars with a shell zero — one of the earliest true zeros.