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Number

638

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

Arithmetic Number Deficient Number Happy Number Odious Number Pernicious Number Recamán's Sequence Sphenic Number Squarefree Year

Notable events — 638 AD

Undated Caliph Umar's forces capture Jerusalem from the Byzantines.

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

Historical context — 638 BC

Calendar year

The year 638 BC was a year of the pre-Julian Roman calendar.

Excerpt from Wikipedia (en) ↗ · Licensed CC BY-SA 4.0 · English fallback 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: Monday
January 1, 638
Ended on: Monday
December 31, 638
Friday the 13ths: 2
2 Friday the 13ths this year.
Decade: 630s
630–639
Century: 7th century
601–700
Millennium: 1st millennium
1–1000
Years ago: 1,388
1388 years before 2026.

In other calendars

Hebrew: 4398 / 4399 AM
Rosh Hashanah falls in September/October.
Islamic Hijri: 16 / 17 AH
Lunar calendar; year spans differ from Gregorian.
Chinese: Year of the zodiac:Earth zodiac:Dog
Sexagenary cycle position 35 of 60. Lunar new year falls in late January / mid-February.
Buddhist Era: 1181 BE
Counted from the parinirvana of the Buddha (Theravada / Thai / Sri Lankan convention).
Persian Solar Hijri: 16 / 17 SH
Iranian calendar; Nowruz (new year) falls on the spring equinox.
Ethiopian: 630 / 631 ET
Year boundary at Enkutatash (September 11/12).
Indian National (Saka): 560 / 559 Saka
Indian national calendar; year starts in March.

Properties

Parity: Even
Digit count: 3
Digit sum: 17
Digit product: 144
Digital root: 8
Palindrome: No
Bit width: 10 bits
Reversed: 836
Recamán's sequence: a(4,643) = 638
Square (n²): 407,044
Cube (n³): 259,694,072
Divisor count: 8
σ(n) — sum of divisors: 1,080
φ(n) — Euler's totient: 280
Sum of prime factors: 42

Primality

Prime factorization: 2 × 11 × 29

Nearest primes: 631 (−7) · 641 (+3)

Divisors & multiples

All divisors (8)

1 · 2 · 11 · 22 · 29 · 58 · 319 (half) · 638

Aliquot sum (sum of proper divisors): 442

Factor pairs (a × b = 638)

1 × 638

2 × 319

11 × 58

22 × 29

First multiples

638 · 1,276 (double) · 1,914 · 2,552 · 3,190 · 3,828 · 4,466 · 5,104 · 5,742 · 6,380

Sums & aliquot sequence

As consecutive integers: 158 + 159 + 160 + 161 53 + 54 + … + 63 8 + 9 + … + 36

Aliquot sequence: 638 → 442 → 314 → 160 → 218 → 112 → 136 → 134 → 70 → 74 → 40 → 50 → 43 → 1 → 0 — terminates at zero

Representations

In words: six hundred thirty-eight
Ordinal: 638th
Roman numeral: DCXXXVIII
Binary: 1001111110
Octal: 1176
Hexadecimal: 0x27E
Base64: An4=
One's complement: 64,897 (16-bit)

In other bases

ternary (3) 212122

quaternary (4) 21332

quinary (5) 10023

senary (6) 2542

septenary (7) 1601

nonary (9) 778

undecimal (11) 530

duodecimal (12) 452

tridecimal (13) 3a1

tetradecimal (14) 338

pentadecimal (15) 2c8

Historical numeral systems

Babylonian (base 60): 𒌋 𒌋𒌋𒌋𒁹𒁹𒁹𒁹𒁹𒁹𒁹𒁹
Egyptian hieroglyphic: 𓍢𓍢𓍢𓍢𓍢𓍢𓎆𓎆𓎆𓏺𓏺𓏺𓏺𓏺𓏺𓏺𓏺
Greek (Milesian): χληʹ
Mayan (base 20): 𝋡·𝋫·𝋲
Chinese: 六百三十八
Chinese (financial): 陸佰參拾捌

In other modern scripts

Eastern Arabic ٦٣٨ Devanagari ६३८ Bengali ৬৩৮ Tamil ௬௩௮ Thai ๖๓๘ Tibetan ༦༣༨ Khmer ៦៣៨ Lao ໖໓໘ Burmese ၆၃၈

Digit at this position in famous constants

π — Pi (π): Digit 638 = 6
e — Euler's number (e): Digit 638 = 2
φ — Golden ratio (φ): Digit 638 = 2
√2 — Pythagoras's (√2): Digit 638 = 8
ln 2 — Natural log of 2: Digit 638 = 0
γ — Euler-Mascheroni (γ): Digit 638 = 8

Also seen as

Goldbach decomposition

Goldbach's conjecture says every even integer greater than 2 is the sum of two primes. For 638, here are decompositions:

7 + 631 = 638
19 + 619 = 638
31 + 607 = 638
37 + 601 = 638
61 + 577 = 638
67 + 571 = 638
97 + 541 = 638
139 + 499 = 638

Showing the first eight; more decompositions exist.

Unicode codepoint

ɾ

Latin Small Letter R With Fishhook

U+027E

Lowercase letter (Ll)

UTF-8 encoding: C9 BE (2 bytes).

Lookup U+027E on Compart ↗ Lookup on FileFormat.Info ↗

Hex color

#00027E

RGB(0, 2, 126)

IPv4 address

As an unsigned 32-bit integer, this is the IPv4 address 0.0.2.126.

Address: 0.0.2.126
Class: reserved
IPv4-mapped IPv6: ::ffff:0.0.2.126

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