668
668 is a composite number, even, a calendar year.
Historical context — 668 AD
Calendar year
Year 668 (DCLXVIII) was a leap year starting on Saturday of the Julian calendar.
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Historical context — 668 BC
Calendar year
The year 668 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
-
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, 668
- Ended on
-
Thursday
December 31, 668
- Friday the 13ths
-
2
2 Friday the 13ths this year.
- Decade
-
660s
660–669
- Century
-
7th century
601–700
- Millennium
-
1st millennium
1–1000
- Years ago
-
1,358
1358 years before 2026.
In other calendars
- Hebrew
-
4428 / 4429 AM
Rosh Hashanah falls in September/October.
- Islamic Hijri
-
47 / 48 AH
Lunar calendar; year spans differ from Gregorian.
- Chinese
-
Year of the zodiac:Earth zodiac:Dragon
Sexagenary cycle position 5 of 60. Lunar new year falls in late January / mid-February.
- Buddhist Era
-
1211 BE
Counted from the parinirvana of the Buddha (Theravada / Thai / Sri Lankan convention).
- Persian Solar Hijri
-
46 / 47 SH
Iranian calendar; Nowruz (new year) falls on the spring equinox.
- Ethiopian
-
660 / 661 ET
Year boundary at Enkutatash (September 11/12).
- Indian National (Saka)
-
590 / 589 Saka
Indian national calendar; year starts in March.
Properties
- Parity
- Even
- Digit count
- 3
- Digit sum
- 20
- Digit product
- 288
- Digital root
- 2
- Palindrome
- No
- Bit width
- 10 bits
- Reversed
- 866
- Flips to (rotate 180°)
- 899
- Recamán's sequence
- a(2,288) = 668
- Square (n²)
- 446,224
- Cube (n³)
- 298,077,632
- Divisor count
- 6
- σ(n) — sum of divisors
- 1,176
- φ(n) — Euler's totient
- 332
- Sum of prime factors
- 171
Primality
Prime factorization: 2 2 × 167
Divisors & multiples
Sums & aliquot sequence
Representations
- In words
- six hundred sixty-eight
- Ordinal
- 668th
- Roman numeral
- DCLXVIII
- Binary
- 1010011100
- Octal
- 1234
- Hexadecimal
- 0x29C
- Base64
- Apw=
- One's complement
- 64,867 (16-bit)
Historical numeral systems
- Babylonian (base 60)
- 𒌋𒁹 𒁹𒁹𒁹𒁹𒁹𒁹𒁹𒁹
- Egyptian hieroglyphic
- 𓍢𓍢𓍢𓍢𓍢𓍢𓎆𓎆𓎆𓎆𓎆𓎆𓏺𓏺𓏺𓏺𓏺𓏺𓏺𓏺
- Greek (Milesian)
- χξηʹ
- Mayan (base 20)
- 𝋡·𝋭·𝋨
- Chinese
- 六百六十八
- Chinese (financial)
- 陸佰陸拾捌
Digit at this position in famous constants
- π — Pi (π)
- Digit 668 = 4
- e — Euler's number (e)
- Digit 668 = 8
- φ — Golden ratio (φ)
- Digit 668 = 8
- √2 — Pythagoras's (√2)
- Digit 668 = 8
- ln 2 — Natural log of 2
- Digit 668 = 0
- γ — Euler-Mascheroni (γ)
- Digit 668 = 9
Also seen as
Goldbach's conjecture says every even integer greater than 2 is the sum of two primes. For 668, here are decompositions:
- 7 + 661 = 668
- 37 + 631 = 668
- 61 + 607 = 668
- 67 + 601 = 668
- 97 + 571 = 668
- 127 + 541 = 668
- 181 + 487 = 668
- 211 + 457 = 668
Showing the first eight; more decompositions exist.
UTF-8 encoding: CA 9C (2 bytes).
As an unsigned 32-bit integer, this is the IPv4 address 0.0.2.156.
- Address
- 0.0.2.156
- Class
- reserved
- IPv4-mapped IPv6
- ::ffff:0.0.2.156
Unspecified address (0.0.0.0/8) — "this network" placeholder.