621
621 is a composite number, odd, a calendar year.
621 (six hundred twenty-one) is an odd 3-digit number. It is a composite number with 8 divisors, and factors as 3³ × 23. Written other ways, in Roman numerals it is DCXXI and in binary, 1001101101.
Interestingness
Historical context — 621 AD
Calendar year
Year 621 (DCXXI) was a common year starting on Thursday of the Julian calendar.
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Historical context — 621 BC
Calendar year
The year 621 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, 621
- Ended on
-
Monday
December 31, 621
- Friday the 13ths
-
2
2 Friday the 13ths this year.
- Decade
-
620s
620–629
- Century
-
7th century
601–700
- Millennium
-
1st millennium
1–1000
- Years ago
-
1,405
1405 years before 2026.
In other calendars
- Hebrew
-
4381 / 4382 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
-
1164 BE
Counted from the parinirvana of the Buddha (Theravada / Thai / Sri Lankan convention).
- Ethiopian
-
613 / 614 ET
Year boundary at Enkutatash (September 11/12).
- Indian National (Saka)
-
543 / 542 Saka
Indian national calendar; year starts in March.
Properties
Primality
Prime factorization: 3 3 × 23
Divisors & multiples
Sums & aliquot sequence
Continued fraction of √n
√621 = [24; (1, 11, 2, 11, 1, 48)]
Period length 6 — the block in parentheses repeats forever.
Representations
- In words
- six hundred twenty-one
- Ordinal
- 621st
- Roman numeral
- DCXXI
- Binary
- 1001101101
- Octal
- 1155
- Hexadecimal
- 0x26D
- Base64
- Am0=
- One's complement
- 64,914 (16-bit)
- Scientific notation
- 6.21 × 10²
- As a duration
- 621 s = 10 minutes, 21 seconds
As an angle
Historical numeral systems
- Babylonian (base 60)
- 𒌋 𒌋𒌋𒁹
- Egyptian hieroglyphic
- 𓍢𓍢𓍢𓍢𓍢𓍢𓎆𓎆𓏺
- Greek (Milesian)
- χκαʹ
- Mayan (base 20)
- 𝋡·𝋫·𝋡
- Chinese
- 六百二十一
- Chinese (financial)
- 陸佰貳拾壹
Digit at this position in famous constants
- π — Pi (π)
- Digit 621 = 2
- e — Euler's number (e)
- Digit 621 = 9
- φ — Golden ratio (φ)
- Digit 621 = 4
- √2 — Pythagoras's (√2)
- Digit 621 = 0
- ln 2 — Natural log of 2
- Digit 621 = 5
- γ — Euler-Mascheroni (γ)
- Digit 621 = 2
Also seen as
UTF-8 encoding: C9 AD (2 bytes).
As an unsigned 32-bit integer, this is the IPv4 address 0.0.2.109.
- Address
- 0.0.2.109
- Class
- reserved
- IPv4-mapped IPv6
- ::ffff:0.0.2.109
Unspecified address (0.0.0.0/8) — "this network" placeholder.
Heard as a frequency, 621 Hz is closest to:
- Concert pitch (A4 = 440 Hz): D♯5 (622.3 Hz, -3¢)
- Scientific pitch (C4 = 256 Hz): D♯5 (608.9 Hz, +34¢)
- Baroque pitch (A4 = 415 Hz): E5 (621.8 Hz, -2¢)
On an ingredients label, E621 is Monosodium glutamate, a flavour enhancer — MSG, the savoury “umami” enhancer.
Related reading
- Babylonian numerals — The base-60 cuneiform system that gave us 60 minutes, 60 seconds, and 360°.