646
ISO 646 is the international standard that ASCII is a variant of.
- Even
- Composite
Where 646 fits
Why 646 is special
National variants replaced characters like backslash and braces with accented letters, which is why early C code was sometimes unwritable on European terminals and why trigraph escapes exist in the language.
646 is part of
Factors & digit properties
- Divisors (8)
- 1, 2, 17, 19, 34, 38, 323, 646
- Prime factorisation
- 2 × 17 × 19
- Digit sum
- 16
- Digital root
- 7
Representations
- Decimal
- 646
- Scientific notation
- 6.460 × 10^2
Roman numerals
D C X L V I
DCXLVI uses the subtractive pair XL: ten before fifty — fifty minus ten.
Binary
1 0 1 0 0 0 0 1 1 0
1 × 512 + 0 × 256 + 1 × 128 + 0 × 64 + 0 × 32 + 0 × 16 + 0 × 8 + 1 × 4 + 1 × 2 + 0 × 1 = 646
Octal
1 2 0 6
1 × 512 + 2 × 64 + 0 × 8 + 6 × 1 = 646
Hexadecimal
2 8 6
2 × 256 + 8 × 16 + 6 × 1 = 646
Read as powers of two: 512 + 128 + 4 + 2 = 646.
In historical numeral systems
Egyptian
6 coils of rope, 4 hobbles, 6 strokes
6 × 100 + 4 × 10 + 6 × 1 = 646. The signs are simply repeated and added; where they sit on the line is a matter of layout, not value.
Babylonian
1 corner wedge (sixties place), 4 corner wedges + 6 vertical wedges (units place)
10 × 60 + 46 = 646. Places are separated by a space on the tablet, with the higher place written first.
Greek (Ionic)
chi, then mu, then stigma, marked as a numeral
chi-mu-stigma + keraia
chi + mu + stigma 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 mem, then vav
tav-resh-mem-vav
tav (400) + resh (200) + mem (40) + vav (6) = 646, 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
- Palindromic number
- Deficient number
Related numbers & connections
ISO 646 defined national variants of a seven-bit set and ISO 8859 extended to eight bits with sixteen incompatible parts. Both problems were ended by Unicode.
View 8859 →Other connections
- developed from8859
why?
Strength 0.50, confidence "high".
Technology & computing
National ISO 646 variants substituted accented letters for braces and backslashes, making standard C source impossible to type on some terminals. Trigraphs were added to the language purely to work around it.
DocumentedTechnology & computing
Common questions
Is 646 a prime number?
No, 646 is not prime.
What are the factors of 646?
The factors of 646 are 1, 2, 17, 19, 34, 38, 323, 646.
What is 646 in Roman numerals?
646 in Roman numerals is DCXLVI. XL is subtractive: ten before fifty — fifty minus ten. Written additively it would be DCXXXXVI, which Roman inscriptions used freely — the strict subtractive form is a later convention.
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