Number

221

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

221 (two hundred twenty-one) is an odd 3-digit number. It is a composite number with 4 divisors, and factors as 13 × 17. Written other ways, in Roman numerals it is CCXXI and in binary, 11011101.

Arithmetic Number Centered Square Cube-Free Deficient Number Evil Number Recamán's Sequence Semiprime Squarefree Year

Interestingness

★ ★ ★ ★ ☆

6 notable facts · grade B

209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233

less more

Historical context — 221 AD

Calendar year

Year 221 (CCXXI) 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 →

Notable events — 221 BC

Undated Qin Shi Huang unifies China, founding the Qin dynasty.

Events compiled from Wikipedia ↗ · Licensed CC BY-SA 4.0

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, 221
Ended on: Monday
December 31, 221
Friday the 13ths: 2
2 Friday the 13ths this year.
Decade: 220s
220–229
Century: 3rd century
201–300
Millennium: 1st millennium
1–1000
Years ago: 1,805
1805 years before 2026.

In other calendars

Hebrew: 3981 / 3982 AM
Rosh Hashanah falls in September/October.
Chinese: Year of the zodiac:Metal zodiac:Ox
Sexagenary cycle position 38 of 60. Lunar new year falls in late January / mid-February.
Buddhist Era: 764 BE
Counted from the parinirvana of the Buddha (Theravada / Thai / Sri Lankan convention).
Ethiopian: 213 / 214 ET
Year boundary at Enkutatash (September 11/12).
Indian National (Saka): 143 / 142 Saka
Indian national calendar; year starts in March.

Properties

Parity: Odd
Digit count: 3
Digit sum: 5
Digit product: 4
Digital root: 5
Palindrome: No
Bit width: 8 bits
Reversed: 122
Recamán's sequence: a(2,590) = 221
Square (n²): 48,841
Cube (n³): 10,793,861
Divisor count: 4
σ(n) — sum of divisors: 252
φ(n) — Euler's totient: 192
Sum of prime factors: 30

Primality

Prime factorization: 13 × 17

Nearest primes: 211 (−10) · 223 (+2)

Divisors & multiples

All divisors (4)

1 · 13 · 17 · 221

Aliquot sum (sum of proper divisors): 31

Factor pairs (a × b = 221)

1 × 221

13 × 17

First multiples

221 · 442 (double) · 663 · 884 · 1,105 · 1,326 · 1,547 · 1,768 · 1,989 · 2,210

Sums & aliquot sequence

As a sum of two squares: 5² + 14² = 10² + 11²

As consecutive integers: 110 + 111 11 + 12 + … + 23 5 + 6 + … + 21

Aliquot sequence: 221 → 31 → 1 → 0 — terminates at zero

Continued fraction of √n

√221 = [14; (1, 6, 2, 6, 1, 28)]

Period length 6 — the block in parentheses repeats forever.

Representations

In words: two hundred twenty-one
Ordinal: 221st
Roman numeral: CCXXI
Binary: 11011101
Octal: 335
Hexadecimal: 0xDD
Base64: 3Q==
One's complement: 34 (8-bit)
Scientific notation: 2.21 × 10²
As a duration: 221 s = 3 minutes, 41 seconds

In other bases

ternary (3) 22012

quaternary (4) 3131

quinary (5) 1341

senary (6) 1005

septenary (7) 434

nonary (9) 265

undecimal (11) 191

duodecimal (12) 165

tridecimal (13) 140

tetradecimal (14) 11b

pentadecimal (15) eb

Palindromic in base 7, base 11

As an angle

221°

221° ≈ 3.857 rad

Compass bearing: SW (southwest)

Why does a circle have 360 degrees? →

Historical numeral systems

Babylonian (base 60): 𒁹𒁹𒁹 𒌋𒌋𒌋𒌋𒁹
Egyptian hieroglyphic: 𓍢𓍢𓎆𓎆𓏺
Greek (Milesian): σκαʹ
Mayan (base 20): 𝋫·𝋡
Chinese: 二百二十一
Chinese (financial): 貳佰貳拾壹

In other modern scripts

Eastern Arabic ٢٢١ Devanagari २२१ Bengali ২২১ Tamil ௨௨௧ Thai ๒๒๑ Tibetan ༢༢༡ Khmer ២២១ Lao ໒໒໑ Burmese ၂၂၁

Digit at this position in famous constants

π — Pi (π): Digit 221 = 1
e — Euler's number (e): Digit 221 = 0
φ — Golden ratio (φ): Digit 221 = 6
√2 — Pythagoras's (√2): Digit 221 = 5
ln 2 — Natural log of 2: Digit 221 = 4
γ — Euler-Mascheroni (γ): Digit 221 = 8

Also seen as

Unicode codepoint

Latin Capital Letter Y With Acute

U+00DD

Uppercase letter (Lu)

UTF-8 encoding: C3 9D (2 bytes).

Lookup U+00DD on Compart ↗ Lookup on FileFormat.Info ↗

Hex color

#0000DD

RGB(0, 0, 221)

IPv4 address

As an unsigned 32-bit integer, this is the IPv4 address 0.0.0.221.

Address: 0.0.0.221
Class: reserved
IPv4-mapped IPv6: ::ffff:0.0.0.221

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

Musical pitch

Heard as a frequency, 221 Hz is closest to:

Concert pitch (A4 = 440 Hz): A3 (220 Hz, +8¢)
Scientific pitch (C4 = 256 Hz): A3 (215.3 Hz, +45¢ — about midway to A♯3)
Baroque pitch (A4 = 415 Hz): A♯3 (219.8 Hz, +9¢)