Number

640

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

640 (six hundred forty) is an even 3-digit number. It is a composite number with 16 divisors, and factors as 2⁷ × 5. Its proper divisors sum to 890, more than the number itself, making it an abundant number. Written other ways, in Roman numerals it is DCXL and in binary, 1010000000.

Abundant Number Descending Digits Evil Number Harshad / Niven Pernicious Number Practical Number Recamán's Sequence Refactorable Number Semiperfect Number Year

Interestingness

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6 notable facts · grade B

628 629 630 631 632 633 634 635 636 637 638 639 640 641 642 643 644 645 646 647 648 649 650 651 652

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Historical context — 640 AD

Calendar year

Year 640 (DCXL) was a leap year starting on Saturday of the Julian calendar.

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

Historical context — 640 BC

Calendar year

The year 640 BC was a year of the pre-Julian Roman calendar.

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

Year facts

Year type: Leap year
Divisible by 4 and not by 100; February has 29 days.
Days in year: 366
ISO weeks: 53
Long year: contains 53 ISO weeks.
Started on: Wednesday
January 1, 640
Ended on: Thursday
December 31, 640
Friday the 13ths: 2
2 Friday the 13ths this year.
Decade: 640s
640–649
Century: 7th century
601–700
Millennium: 1st millennium
1–1000
Years ago: 1,386
1386 years before 2026.

In other calendars

Hebrew: 4400 / 4401 AM
Rosh Hashanah falls in September/October.
Islamic Hijri: 18 / 20 AH
Lunar calendar; year spans differ from Gregorian.
Chinese: Year of the zodiac:Metal zodiac:Rat
Sexagenary cycle position 37 of 60. Lunar new year falls in late January / mid-February.
Buddhist Era: 1183 BE
Counted from the parinirvana of the Buddha (Theravada / Thai / Sri Lankan convention).
Persian Solar Hijri: 18 / 19 SH
Iranian calendar; Nowruz (new year) falls on the spring equinox.
Ethiopian: 632 / 633 ET
Year boundary at Enkutatash (September 11/12).
Indian National (Saka): 562 / 561 Saka
Indian national calendar; year starts in March.

Properties

Parity: Even
Digit count: 3
Digit sum: 10
Digit product: 0
Digital root: 1
Palindrome: No
Bit width: 10 bits
Reversed: 46
Recamán's sequence: a(4,639) = 640
Square (n²): 409,600
Cube (n³): 262,144,000
Divisor count: 16
σ(n) — sum of divisors: 1,530
φ(n) — Euler's totient: 256
Sum of prime factors: 19

Primality

Prime factorization: 2 ⁷ × 5

Nearest primes: 631 (−9) · 641 (+1)

Divisors & multiples

All divisors (16)

1 · 2 · 4 · 5 · 8 · 10 · 16 · 20 · 32 · 40 · 64 · 80 · 128 · 160 · 320 (half) · 640

Aliquot sum (sum of proper divisors): 890

Factor pairs (a × b = 640)

1 × 640

2 × 320

4 × 160

5 × 128

8 × 80

10 × 64

16 × 40

20 × 32

First multiples

640 · 1,280 (double) · 1,920 · 2,560 · 3,200 · 3,840 · 4,480 · 5,120 · 5,760 · 6,400

Sums & aliquot sequence

As a sum of two squares: 8² + 24²

As consecutive integers: 126 + 127 + 128 + 129 + 130

Aliquot sequence: 640 → 890 → 730 → 602 → 454 → 230 → 202 → 104 → 106 → 56 → 64 → 63 → 41 → 1 → 0 — terminates at zero

Continued fraction of √n

√640 = [25; (3, 2, 1, 4, 1, 11, 1, 4, 1, 2, 3, 50)]

Period length 12 — the block in parentheses repeats forever.

Representations

In words: six hundred forty
Ordinal: 640th
Roman numeral: DCXL
Binary: 1010000000
Octal: 1200
Hexadecimal: 0x280
Base64: AoA=
One's complement: 64,895 (16-bit)
Scientific notation: 6.4 × 10²
As a duration: 640 s = 10 minutes, 40 seconds

In other bases

ternary (3) 212201

quaternary (4) 22000

quinary (5) 10030

senary (6) 2544

septenary (7) 1603

nonary (9) 781

undecimal (11) 532

duodecimal (12) 454

tridecimal (13) 3a3

tetradecimal (14) 33a

pentadecimal (15) 2ca

Palindromic in base 12, base 13

As an angle

640° = 1 × 360° + 280°

280° ≈ 4.887 rad

Compass bearing: W (west)

Why does a circle have 360 degrees? →

Historical numeral systems

Babylonian (base 60): 𒌋 𒌋𒌋𒌋𒌋
Egyptian hieroglyphic: 𓍢𓍢𓍢𓍢𓍢𓍢𓎆𓎆𓎆𓎆
Greek (Milesian): χμʹ
Mayan (base 20): 𝋡·𝋬·𝋠
Chinese: 六百四十
Chinese (financial): 陸佰肆拾

In other modern scripts

Eastern Arabic ٦٤٠ Devanagari ६४० Bengali ৬৪০ Tamil ௬௪௦ Thai ๖๔๐ Tibetan ༦༤༠ Khmer ៦៤០ Lao ໖໔໐ Burmese ၆၄၀

Digit at this position in famous constants

π — Pi (π): Digit 640 = 9
e — Euler's number (e): Digit 640 = 2
φ — Golden ratio (φ): Digit 640 = 7
√2 — Pythagoras's (√2): Digit 640 = 9
ln 2 — Natural log of 2: Digit 640 = 7
γ — Euler-Mascheroni (γ): Digit 640 = 4

Also seen as

Goldbach decomposition

Goldbach's conjecture says every even integer greater than 2 is the sum of two primes. For 640, here are decompositions:

23 + 617 = 640
41 + 599 = 640
47 + 593 = 640
53 + 587 = 640
71 + 569 = 640
83 + 557 = 640
131 + 509 = 640
137 + 503 = 640

Showing the first eight; more decompositions exist.

Unicode codepoint

Latin Letter Small Capital R

U+0280

Lowercase letter (Ll)

UTF-8 encoding: CA 80 (2 bytes).

Lookup U+0280 on Compart ↗ Lookup on FileFormat.Info ↗

Hex color

#000280

RGB(0, 2, 128)

IPv4 address

As an unsigned 32-bit integer, this is the IPv4 address 0.0.2.128.

Address: 0.0.2.128
Class: reserved
IPv4-mapped IPv6: ::ffff:0.0.2.128

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

Musical pitch

Heard as a frequency, 640 Hz is closest to:

Concert pitch (A4 = 440 Hz): D♯5 (622.3 Hz, +49¢ — about midway to E5)
Scientific pitch (C4 = 256 Hz): E5 (645.1 Hz, -14¢)
Baroque pitch (A4 = 415 Hz): E5 (621.8 Hz, +50¢ — about midway to F5)