Number

646

646 is a composite number, even, a calendar year.

Arithmetic Number Deficient Number Evil Number Palindrome Recamán's Sequence Sphenic Number Squarefree Year

Historical context — 646 AD

Calendar year

Year 646 (DCXLVI) was a common year starting on Sunday of the Julian calendar.

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Historical context — 646 BC

Decade

This article concerns the period 649 BC – 640 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: 53
Long year: contains 53 ISO weeks.
Started on: Thursday
January 1, 646
Ended on: Thursday
December 31, 646
Friday the 13ths: 3
3 Friday the 13ths this year.
Decade: 640s
640–649
Century: 7th century
601–700
Millennium: 1st millennium
1–1000
Years ago: 1,380
1380 years before 2026.

In other calendars

Hebrew: 4406 / 4407 AM
Rosh Hashanah falls in September/October.
Islamic Hijri: 25 / 26 AH
Lunar calendar; year spans differ from Gregorian.
Chinese: Year of the zodiac:Fire zodiac:Horse
Sexagenary cycle position 43 of 60. Lunar new year falls in late January / mid-February.
Buddhist Era: 1189 BE
Counted from the parinirvana of the Buddha (Theravada / Thai / Sri Lankan convention).
Persian Solar Hijri: 24 / 25 SH
Iranian calendar; Nowruz (new year) falls on the spring equinox.
Ethiopian: 638 / 639 ET
Year boundary at Enkutatash (September 11/12).
Indian National (Saka): 568 / 567 Saka
Indian national calendar; year starts in March.

Properties

Parity: Even
Digit count: 3
Digit sum: 16
Digit product: 144
Digital root: 7
Palindrome: Yes
Bit width: 10 bits
Recamán's sequence: a(2,332) = 646
Square (n²): 417,316
Cube (n³): 269,586,136
Divisor count: 8
σ(n) — sum of divisors: 1,080
φ(n) — Euler's totient: 288
Sum of prime factors: 38

Primality

Prime factorization: 2 × 17 × 19

Nearest primes: 643 (−3) · 647 (+1)

Divisors & multiples

All divisors (8)

1 · 2 · 17 · 19 · 34 · 38 · 323 (half) · 646

Aliquot sum (sum of proper divisors): 434

Factor pairs (a × b = 646)

1 × 646

2 × 323

17 × 38

19 × 34

First multiples

646 · 1,292 (double) · 1,938 · 2,584 · 3,230 · 3,876 · 4,522 · 5,168 · 5,814 · 6,460

Sums & aliquot sequence

As consecutive integers: 160 + 161 + 162 + 163 30 + 31 + … + 46 25 + 26 + … + 43

Aliquot sequence: 646 → 434 → 334 → 170 → 154 → 134 → 70 → 74 → 40 → 50 → 43 → 1 → 0 — terminates at zero

Representations

In words: six hundred forty-six
Ordinal: 646th
Roman numeral: DCXLVI
Binary: 1010000110
Octal: 1206
Hexadecimal: 0x286
Base64: AoY=
One's complement: 64,889 (16-bit)

In other bases

ternary (3) 212221

quaternary (4) 22012

quinary (5) 10041

senary (6) 2554

septenary (7) 1612

nonary (9) 787

undecimal (11) 538

duodecimal (12) 45a

tridecimal (13) 3a9

tetradecimal (14) 342

pentadecimal (15) 2d1

Historical numeral systems

Babylonian (base 60): 𒌋 𒌋𒌋𒌋𒌋𒁹𒁹𒁹𒁹𒁹𒁹
Egyptian hieroglyphic: 𓍢𓍢𓍢𓍢𓍢𓍢𓎆𓎆𓎆𓎆𓏺𓏺𓏺𓏺𓏺𓏺
Greek (Milesian): χμϛʹ
Mayan (base 20): 𝋡·𝋬·𝋦
Chinese: 六百四十六
Chinese (financial): 陸佰肆拾陸

In other modern scripts

Eastern Arabic ٦٤٦ Devanagari ६४६ Bengali ৬৪৬ Tamil ௬௪௬ Thai ๖๔๖ Tibetan ༦༤༦ Khmer ៦៤៦ Lao ໖໔໖ Burmese ၆၄၆

Digit at this position in famous constants

π — Pi (π): Digit 646 = 7
e — Euler's number (e): Digit 646 = 4
φ — Golden ratio (φ): Digit 646 = 1
√2 — Pythagoras's (√2): Digit 646 = 7
ln 2 — Natural log of 2: Digit 646 = 1
γ — Euler-Mascheroni (γ): Digit 646 = 4

Also seen as

Goldbach decomposition

Goldbach's conjecture says every even integer greater than 2 is the sum of two primes. For 646, here are decompositions:

3 + 643 = 646
5 + 641 = 646
29 + 617 = 646
47 + 599 = 646
53 + 593 = 646
59 + 587 = 646
83 + 563 = 646
89 + 557 = 646

Showing the first eight; more decompositions exist.

Unicode codepoint

Latin Small Letter Esh With Curl

U+0286

Lowercase letter (Ll)

UTF-8 encoding: CA 86 (2 bytes).

Lookup U+0286 on Compart ↗ Lookup on FileFormat.Info ↗

Hex color

#000286

RGB(0, 2, 134)

IPv4 address

As an unsigned 32-bit integer, this is the IPv4 address 0.0.2.134.

Address: 0.0.2.134
Class: reserved
IPv4-mapped IPv6: ::ffff:0.0.2.134

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

NANP area code 646

The number 646 is an active NANP area code (North American Numbering Plan).

Primary area: Manhattan
Region: New York
Country: United States

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 646 ↗