173
E173 is aluminium, used as a surface colour.
- Odd
- Prime
Where 173 fits
Why 173 is special
It is permitted only for external decoration of confectionery, which is a narrower authorisation than most additives carry.
173 is part of
Factors & digit properties
- Divisors (2)
- 1, 173
- Prime factorisation
- 173
- Digit sum
- 11
- Digital root
- 2
Representations
- Decimal
- 173
- Scientific notation
- 1.730 × 10^2
Roman numerals
C L X X I I I
Binary
1 0 1 0 1 1 0 1
1 × 128 + 0 × 64 + 1 × 32 + 0 × 16 + 1 × 8 + 1 × 4 + 0 × 2 + 1 × 1 = 173
Octal
2 5 5
2 × 64 + 5 × 8 + 5 × 1 = 173
Hexadecimal
a d
a × 16 + d × 1 = 173
Read as powers of two: 128 + 32 + 8 + 4 + 1 = 173.
In historical numeral systems
Egyptian
1 coil of rope, 7 hobbles, 3 strokes
1 × 100 + 7 × 10 + 3 × 1 = 173. 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 + 3 vertical wedges (units place)
2 × 60 + 53 = 173. Places are separated by a space on the tablet, with the higher place written first.
Greek (Ionic)
rho, then omicron, then gamma, marked as a numeral
rho-omicron-gamma + keraia
rho + omicron + gamma 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 gimel
qof-ayin-gimel
qof (100) + ayin (70) + gimel (3) = 173, written in descending order.
Maya
1 bar + 3 dots (upper, twenties place) over 2 bars + 3 dots (lower, units place)
8 × 20 + 13 = 173. 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
- Deficient number
- Sophie Germain prime
Related numbers & connections
Both are metal-based colours whose authorisation is narrower than most additives carry.
View 171 →Other connections
- is associated with171
why?
Strength 0.50, confidence "high".
Everyday life
E173 aluminium is authorised in the European Union only for external coating of sugar confectionery and for decoration of cakes and pastries, not for incorporation into food.
DocumentedEveryday lifeGeography: European Union and states adopting the E number systemPeriod: 1962–
Common questions
Is 173 a prime number?
Yes, 173 is prime — it has exactly two positive divisors: 1 and itself.
What are the factors of 173?
The factors of 173 are 1, 173.
What is 173 in Roman numerals?
173 in Roman numerals is CLXXIII.
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