381
381 is a composite number, odd, a calendar year.
381 (three hundred eighty-one) is an odd 3-digit number. It is a composite number with 4 divisors, and factors as 3 × 127. Written other ways, in Roman numerals it is CCCLXXXI and in binary, 101111101.
Interestingness
Historical context — 381 AD
Calendar year
Year 381 (CCCLXXXI) was a common year starting on Friday of the Julian calendar.
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Historical context — 381 BC
Calendar year
Year 381 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
-
53
Long year: contains 53 ISO weeks.
- Started on
-
Thursday
January 1, 381
- Ended on
-
Thursday
December 31, 381
- Friday the 13ths
-
3
3 Friday the 13ths this year.
- Decade
-
380s
380–389
- Century
-
4th century
301–400
- Millennium
-
1st millennium
1–1000
- Years ago
-
1,645
1645 years before 2026.
In other calendars
- Hebrew
-
4141 / 4142 AM
Rosh Hashanah falls in September/October.
- Chinese
-
Year of the zodiac:Metal zodiac:Snake
Sexagenary cycle position 18 of 60. Lunar new year falls in late January / mid-February.
- Buddhist Era
-
924 BE
Counted from the parinirvana of the Buddha (Theravada / Thai / Sri Lankan convention).
- Ethiopian
-
373 / 374 ET
Year boundary at Enkutatash (September 11/12).
- Indian National (Saka)
-
303 / 302 Saka
Indian national calendar; year starts in March.
Properties
Primality
Prime factorization: 3 × 127
Divisors & multiples
Sums & aliquot sequence
Continued fraction of √n
√381 = [19; (1, 1, 12, 1, 1, 38)]
Period length 6 — the block in parentheses repeats forever.
Representations
- In words
- three hundred eighty-one
- Ordinal
- 381st
- Roman numeral
- CCCLXXXI
- Binary
- 101111101
- Octal
- 575
- Hexadecimal
- 0x17D
- Base64
- AX0=
- One's complement
- 65,154 (16-bit)
- Scientific notation
- 3.81 × 10²
- As a duration
- 381 s = 6 minutes, 21 seconds
As an angle
Historical numeral systems
- Babylonian (base 60)
- 𒁹𒁹𒁹𒁹𒁹𒁹 𒌋𒌋𒁹
- Egyptian hieroglyphic
- 𓍢𓍢𓍢𓎆𓎆𓎆𓎆𓎆𓎆𓎆𓎆𓏺
- Greek (Milesian)
- τπαʹ
- Mayan (base 20)
- 𝋳·𝋡
- Chinese
- 三百八十一
- Chinese (financial)
- 參佰捌拾壹
Digit at this position in famous constants
- π — Pi (π)
- Digit 381 = 2
- e — Euler's number (e)
- Digit 381 = 4
- φ — Golden ratio (φ)
- Digit 381 = 1
- √2 — Pythagoras's (√2)
- Digit 381 = 1
- ln 2 — Natural log of 2
- Digit 381 = 8
- γ — Euler-Mascheroni (γ)
- Digit 381 = 9
Also seen as
UTF-8 encoding: C5 BD (2 bytes).
As an unsigned 32-bit integer, this is the IPv4 address 0.0.1.125.
- Address
- 0.0.1.125
- Class
- reserved
- IPv4-mapped IPv6
- ::ffff:0.0.1.125
Unspecified address (0.0.0.0/8) — "this network" placeholder.
Heard as a frequency, 381 Hz is closest to:
- Concert pitch (A4 = 440 Hz): G4 (392 Hz, -49¢ — about midway to F♯4)
- Scientific pitch (C4 = 256 Hz): G4 (383.6 Hz, -12¢)
- Baroque pitch (A4 = 415 Hz): G♯4 (391.7 Hz, -48¢ — about midway to G4)
Related reading
- Babylonian numerals — The base-60 cuneiform system that gave us 60 minutes, 60 seconds, and 360°.