Number

921

921 is a composite number, odd, a calendar year.

921 (nine hundred twenty-one) is an odd 3-digit number. It is a composite number with 4 divisors, and factors as 3 × 307. Written other ways, in Roman numerals it is CMXXI and in binary, 1110011001.

Arithmetic Number Cube-Free Deficient Number Descending Digits Evil Number Happy Number Recamán's Sequence Semiprime Squarefree Year

Interestingness

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7 notable facts · grade B

909 910 911 912 913 914 915 916 917 918 919 920 921 922 923 924 925 926 927 928 929 930 931 932 933

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Historical context — 921 AD

Calendar year

Year 921 (CMXXI) was a common year starting on Monday of the Julian calendar.

Excerpt from Wikipedia (en) ↗ · Licensed CC BY-SA 4.0 Read the full article on Wikipedia →

Historical context — 921 BC

Decade

The 920s BC is a decade that lasted from 929 BC to 920 BC.

Excerpt from Wikipedia (en) ↗ · Licensed CC BY-SA 4.0 Read the full article on Wikipedia →

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, 921
Ended on: Wednesday
December 31, 921
Friday the 13ths: 1
One Friday the 13th this year.
Decade: 920s
920–929
Century: 10th century
901–1000
Millennium: 1st millennium
1–1000
Years ago: 1,105
1105 years before 2026.

In other calendars

Hebrew: 4681 / 4682 AM
Rosh Hashanah falls in September/October.
Islamic Hijri: 308 / 309 AH
Lunar calendar; year spans differ from Gregorian.
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: 1464 BE
Counted from the parinirvana of the Buddha (Theravada / Thai / Sri Lankan convention).
Persian Solar Hijri: 299 / 300 SH
Iranian calendar; Nowruz (new year) falls on the spring equinox.
Ethiopian: 913 / 914 ET
Year boundary at Enkutatash (September 11/12).
Indian National (Saka): 843 / 842 Saka
Indian national calendar; year starts in March.

Properties

Parity: Odd
Digit count: 3
Digit sum: 12
Digit product: 18
Digital root: 3
Palindrome: No
Bit width: 10 bits
Reversed: 129
Recamán's sequence: a(593) = 921
Square (n²): 848,241
Cube (n³): 781,229,961
Divisor count: 4
σ(n) — sum of divisors: 1,232
φ(n) — Euler's totient: 612
Sum of prime factors: 310

Primality

Prime factorization: 3 × 307

Nearest primes: 919 (−2) · 929 (+8)

Divisors & multiples

All divisors (4)

1 · 3 · 307 · 921

Aliquot sum (sum of proper divisors): 311

Factor pairs (a × b = 921)

1 × 921

3 × 307

First multiples

921 · 1,842 (double) · 2,763 · 3,684 · 4,605 · 5,526 · 6,447 · 7,368 · 8,289 · 9,210

Sums & aliquot sequence

As consecutive integers: 460 + 461 306 + 307 + 308 151 + 152 + 153 + 154 + 155 + 156

Aliquot sequence: 921 → 311 → 1 → 0 — terminates at zero

Continued fraction of √n

√921 = [30; (2, 1, 6, 1, 11, 3, 1, 2, 2, 3, 1, 1, 1, 1, 1, 8, 20, 8, 1, 1, 1, 1, 1, 3, …)]

Period length 34 — the block in parentheses repeats forever.

Representations

In words: nine hundred twenty-one
Ordinal: 921st
Roman numeral: CMXXI
Binary: 1110011001
Octal: 1631
Hexadecimal: 0x399
Base64: A5k=
One's complement: 64,614 (16-bit)
Scientific notation: 9.21 × 10²
As a duration: 921 s = 15 minutes, 21 seconds

In other bases

ternary (3) 1021010

quaternary (4) 32121

quinary (5) 12141

senary (6) 4133

septenary (7) 2454

nonary (9) 1233

undecimal (11) 768

duodecimal (12) 649

tridecimal (13) 55b

tetradecimal (14) 49b

pentadecimal (15) 416

As an angle

921° = 2 × 360° + 201°

201° ≈ 3.508 rad

Compass bearing: SSW (south-southwest)

Why does a circle have 360 degrees? →

Historical numeral systems

Babylonian (base 60): 𒌋𒁹𒁹𒁹𒁹𒁹 𒌋𒌋𒁹
Egyptian hieroglyphic: 𓍢𓍢𓍢𓍢𓍢𓍢𓍢𓍢𓍢𓎆𓎆𓏺
Greek (Milesian): ϡκαʹ
Mayan (base 20): 𝋢·𝋦·𝋡
Chinese: 九百二十一
Chinese (financial): 玖佰貳拾壹

In other modern scripts

Eastern Arabic ٩٢١ Devanagari ९२१ Bengali ৯২১ Tamil ௯௨௧ Thai ๙๒๑ Tibetan ༩༢༡ Khmer ៩២១ Lao ໙໒໑ Burmese ၉၂၁

Digit at this position in famous constants

π — Pi (π): Digit 921 = 3
e — Euler's number (e): Digit 921 = 1
φ — Golden ratio (φ): Digit 921 = 7
√2 — Pythagoras's (√2): Digit 921 = 1
ln 2 — Natural log of 2: Digit 921 = 5
γ — Euler-Mascheroni (γ): Digit 921 = 5

Also seen as

Unicode codepoint

Greek Capital Letter Iota

U+0399

Uppercase letter (Lu)

UTF-8 encoding: CE 99 (2 bytes).

Lookup U+0399 on Compart ↗ Lookup on FileFormat.Info ↗

Hex color

#000399

RGB(0, 3, 153)

IPv4 address

As an unsigned 32-bit integer, this is the IPv4 address 0.0.3.153.

Address: 0.0.3.153
Class: reserved
IPv4-mapped IPv6: ::ffff:0.0.3.153

Unspecified address (0.0.0.0/8) — "this network" placeholder.

Musical pitch

Heard as a frequency, 921 Hz is closest to:

Concert pitch (A4 = 440 Hz): A♯5 (932.3 Hz, -21¢)
Scientific pitch (C4 = 256 Hz): A♯5 (912.3 Hz, +16¢)
Baroque pitch (A4 = 415 Hz): B5 (931.6 Hz, -20¢)