685
+685 is the international calling code for Samoa.
- Odd
- Composite
Where 685 fits
Why 685 is special
Samoa skipped 30 December 2011 entirely, moving across the international date line to align its working week with Australia and New Zealand.
Factors & digit properties
- Divisors (4)
- 1, 5, 137, 685
- Prime factorisation
- 5 × 137
- Digit sum
- 19
- Digital root
- 1
Representations
- Decimal
- 685
- Scientific notation
- 6.850 × 10^2
Roman numerals
D C L X X X V
Binary
1 0 1 0 1 0 1 1 0 1
1 × 512 + 0 × 256 + 1 × 128 + 0 × 64 + 1 × 32 + 0 × 16 + 1 × 8 + 1 × 4 + 0 × 2 + 1 × 1 = 685
Octal
1 2 5 5
1 × 512 + 2 × 64 + 5 × 8 + 5 × 1 = 685
Hexadecimal
2 a d
2 × 256 + a × 16 + d × 1 = 685
Read as powers of two: 512 + 128 + 32 + 8 + 4 + 1 = 685.
In historical numeral systems
Egyptian
6 coils of rope, 8 hobbles, 5 strokes
6 × 100 + 8 × 10 + 5 × 1 = 685. The signs are simply repeated and added; where they sit on the line is a matter of layout, not value.
Babylonian
1 corner wedge + 1 vertical wedge (sixties place), 2 corner wedges + 5 vertical wedges (units place)
11 × 60 + 25 = 685. Places are separated by a space on the tablet, with the higher place written first.
Greek (Ionic)
chi, then pi, then epsilon, marked as a numeral
chi-pi-epsilon + keraia
chi + pi + epsilon written in descending order and added — the letters carry their values wherever they stand, so this is addition, not place value.
Hebrew numerals
tav, then resh, then pe, then he
tav-resh-pe-he
tav (400) + resh (200) + pe (80) + he (5) = 685, written in descending order.
Systems that simply cannot reach this value are left out. Where a script needs a font most readers do not have, the reading is given instead of the glyphs — see number systems for each system in full.
Other mathematical patterns
- Deficient number
- Semiprime
- Lucky number (mathematical sieve)
Related numbers & connections
Tonga and Samoa are Polynesian neighbours. Tonga was never colonised, and Samoa deleted a whole calendar day in 2011 to change sides of the date line.
View 676 →Geography
+685 reaches Samoa, which deleted a whole calendar day in 2011 to switch sides of the date line. The change aligned its business week with its main trading partners.
DocumentedGeographyGeography: Samoa
Common questions
Is 685 a prime number?
No, 685 is not prime.
What are the factors of 685?
The factors of 685 are 1, 5, 137, 685.
What is 685 in Roman numerals?
685 in Roman numerals is DCLXXXV.
About this page's data
Mathematical facts:computed directly from the number's value — nothing to source or verify externally.
Contextual records: 1 reviewer-confirmed record, sourced and reviewed before publication.
Last reviewed: 15 July 2026