Number

721

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

Arithmetic Number Deficient Number Descending Digits Odious Number Pernicious Number Recamán's Sequence Semiprime Squarefree Year

Historical context — 721 AD

Calendar year

Year 721 (DCCXXI) was a common year starting on Wednesday of the Julian calendar.

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Historical context — 721 BC

Decade

This article concerns the period 729 BC – 720 BC.

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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: Saturday
January 1, 721
Ended on: Saturday
December 31, 721
Friday the 13ths: 1
One Friday the 13th this year.
Decade: 720s
720–729
Century: 8th century
701–800
Millennium: 1st millennium
1–1000
Years ago: 1,305
1305 years before 2026.

In other calendars

Hebrew: 4481 / 4482 AM
Rosh Hashanah falls in September/October.
Islamic Hijri: 102 / 103 AH
Lunar calendar; year spans differ from Gregorian.
Chinese: Year of the zodiac:Metal zodiac:Rooster
Sexagenary cycle position 58 of 60. Lunar new year falls in late January / mid-February.
Buddhist Era: 1264 BE
Counted from the parinirvana of the Buddha (Theravada / Thai / Sri Lankan convention).
Persian Solar Hijri: 99 / 100 SH
Iranian calendar; Nowruz (new year) falls on the spring equinox.
Ethiopian: 713 / 714 ET
Year boundary at Enkutatash (September 11/12).
Indian National (Saka): 643 / 642 Saka
Indian national calendar; year starts in March.

Properties

Parity: Odd
Digit count: 3
Digit sum: 10
Digit product: 14
Digital root: 1
Palindrome: No
Bit width: 10 bits
Reversed: 127
Recamán's sequence: a(229) = 721
Square (n²): 519,841
Cube (n³): 374,805,361
Divisor count: 4
σ(n) — sum of divisors: 832
φ(n) — Euler's totient: 612
Sum of prime factors: 110

Primality

Prime factorization: 7 × 103

Nearest primes: 719 (−2) · 727 (+6)

Divisors & multiples

All divisors (4)

1 · 7 · 103 · 721

Aliquot sum (sum of proper divisors): 111

Factor pairs (a × b = 721)

1 × 721

7 × 103

First multiples

721 · 1,442 (double) · 2,163 · 2,884 · 3,605 · 4,326 · 5,047 · 5,768 · 6,489 · 7,210

Sums & aliquot sequence

As consecutive integers: 360 + 361 100 + 101 + … + 106 45 + 46 + … + 58

Aliquot sequence: 721 → 111 → 41 → 1 → 0 — terminates at zero

Representations

In words: seven hundred twenty-one
Ordinal: 721st
Roman numeral: DCCXXI
Binary: 1011010001
Octal: 1321
Hexadecimal: 0x2D1
Base64: AtE=
One's complement: 64,814 (16-bit)

In other bases

ternary (3) 222201

quaternary (4) 23101

quinary (5) 10341

senary (6) 3201

septenary (7) 2050

nonary (9) 881

undecimal (11) 5a6

duodecimal (12) 501

tridecimal (13) 436

tetradecimal (14) 397

pentadecimal (15) 331

Historical numeral systems

Babylonian (base 60): 𒌋𒁹𒁹 𒁹
Egyptian hieroglyphic: 𓍢𓍢𓍢𓍢𓍢𓍢𓍢𓎆𓎆𓏺
Greek (Milesian): ψκαʹ
Mayan (base 20): 𝋡·𝋰·𝋡
Chinese: 七百二十一
Chinese (financial): 柒佰貳拾壹

In other modern scripts

Eastern Arabic ٧٢١ Devanagari ७२१ Bengali ৭২১ Tamil ௭௨௧ Thai ๗๒๑ Tibetan ༧༢༡ Khmer ៧២១ Lao ໗໒໑ Burmese ၇၂၁

Digit at this position in famous constants

π — Pi (π): Digit 721 = 0
e — Euler's number (e): Digit 721 = 1
φ — Golden ratio (φ): Digit 721 = 5
√2 — Pythagoras's (√2): Digit 721 = 7
ln 2 — Natural log of 2: Digit 721 = 8
γ — Euler-Mascheroni (γ): Digit 721 = 9

Also seen as

Unicode codepoint

Modifier Letter Half Triangular Colon

U+02D1

Modifier letter (Lm)

UTF-8 encoding: CB 91 (2 bytes).

Lookup U+02D1 on Compart ↗ Lookup on FileFormat.Info ↗

Hex color

#0002D1

RGB(0, 2, 209)

IPv4 address

As an unsigned 32-bit integer, this is the IPv4 address 0.0.2.209.

Address: 0.0.2.209
Class: reserved
IPv4-mapped IPv6: ::ffff:0.0.2.209

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

NANP area code 721

The number 721 is an active NANP area code (North American Numbering Plan).

Primary area: Statewide
Region: Sint Maarten
Country: Sint Maarten

Most NANP area codes have multiple overlays in dense regions; the primary area listed is the historic/largest population center for this code.

Look up area code 721 ↗