171
E171 is titanium dioxide, banned as a food additive in the EU.
- Odd
- Composite
Where 171 fits
Why 171 is special
The 2021 EFSA opinion could not rule out genotoxicity from nanoparticles, and the additive was prohibited in food while remaining permitted in medicines and cosmetics.
Factors & digit properties
- Divisors (6)
- 1, 3, 9, 19, 57, 171
- Prime factorisation
- 3^2 × 19
- Digit sum
- 9
- Digital root
- 9
Representations
- Decimal
- 171
- Scientific notation
- 1.710 × 10^2
Roman numerals
C L X X I
Binary
1 0 1 0 1 0 1 1
1 × 128 + 0 × 64 + 1 × 32 + 0 × 16 + 1 × 8 + 0 × 4 + 1 × 2 + 1 × 1 = 171
Octal
2 5 3
2 × 64 + 5 × 8 + 3 × 1 = 171
Hexadecimal
a b
a × 16 + b × 1 = 171
Read as powers of two: 128 + 32 + 8 + 2 + 1 = 171.
In historical numeral systems
Egyptian
1 coil of rope, 7 hobbles, 1 stroke
1 × 100 + 7 × 10 + 1 × 1 = 171. The signs are simply repeated and added; where they sit on the line is a matter of layout, not value.
Babylonian
2 vertical wedges (sixties place), 5 corner wedges + 1 vertical wedge (units place)
2 × 60 + 51 = 171. Places are separated by a space on the tablet, with the higher place written first.
Greek (Ionic)
rho, then omicron, then alpha, marked as a numeral
rho-omicron-alpha + keraia
rho + omicron + alpha written in descending order and added — the letters carry their values wherever they stand, so this is addition, not place value.
Hebrew numerals
qof, then ayin, then alef
qof-ayin-alef
qof (100) + ayin (70) + alef (1) = 171, written in descending order.
Maya
1 bar + 3 dots (upper, twenties place) over 2 bars + 1 dot (lower, units place)
8 × 20 + 11 = 171. Places stack vertically with the smallest at the bottom, so the upper group is worth twenty times the lower.
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
- Triangular number
- Palindromic number
- Deficient number
- Harshad (Niven) number
- Lucky number (mathematical sieve)
Related numbers & connections
E171 is an additive number whose authorisation was withdrawn, so the identifier now records a prohibition.
Both are metal-based colours whose authorisation is narrower than most additives carry.
View 173 →Numbers Around Us
- appears inNumbers assigned as identifiers
why?
Strength 0.50, confidence "high".
Other connections
- is associated with173
why?
Strength 0.50, confidence "high".
Everyday life
E171 titanium dioxide was banned as a food additive in the European Union from 2022 following an EFSA opinion that genotoxicity could not be excluded. It remains authorised in other product categories and in other jurisdictions.
DocumentedEveryday lifeGeography: European Union and states adopting the E number systemPeriod: 1962–
Common questions
Is 171 a prime number?
No, 171 is not prime.
What are the factors of 171?
The factors of 171 are 1, 3, 9, 19, 57, 171.
What is 171 in Roman numerals?
171 in Roman numerals is CLXXI.
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