729
729 is both 3 to the sixth power and 27 squared.
Where 729 fits
Why 729 is special
It is one of the few numbers that is simultaneously a perfect square and a perfect cube below a thousand — the others being 1 and 64. Numbers with that property are sixth powers, which is a small and rapidly thinning set.
729 is part of
Factors & digit properties
- Divisors (7)
- 1, 3, 9, 27, 81, 243, 729
- Prime factorisation
- 3^6
- Digit sum
- 18
- Digital root
- 9
Representations
- Decimal
- 729
- Scientific notation
- 7.290 × 10^2
Roman numerals
D C C X X I X
DCCXXIX uses the subtractive pair IX: one before ten — ten minus one.
Binary
1 0 1 1 0 1 1 0 0 1
1 × 512 + 0 × 256 + 1 × 128 + 1 × 64 + 0 × 32 + 1 × 16 + 1 × 8 + 0 × 4 + 0 × 2 + 1 × 1 = 729
Octal
1 3 3 1
1 × 512 + 3 × 64 + 3 × 8 + 1 × 1 = 729
Hexadecimal
2 d 9
2 × 256 + d × 16 + 9 × 1 = 729
Read as powers of two: 512 + 128 + 64 + 16 + 8 + 1 = 729.
In historical numeral systems
Egyptian
7 coils of rope, 2 hobbles, 9 strokes
7 × 100 + 2 × 10 + 9 × 1 = 729. The signs are simply repeated and added; where they sit on the line is a matter of layout, not value.
Babylonian
1 corner wedge + 2 vertical wedges (sixties place), 9 vertical wedges (units place)
12 × 60 + 9 = 729. Places are separated by a space on the tablet, with the higher place written first.
Greek (Ionic)
psi, then kappa, then theta, marked as a numeral
psi-kappa-theta + keraia
psi + kappa + theta 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 shin, then kaf, then tet
tav-shin-kaf-tet
tav (400) + shin (300) + kaf (20) + tet (9) = 729, 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
- Powerful number
- Lucky number (mathematical sieve)
Related numbers & connections
Both are sixth powers and therefore both square and cube — 64 is 2 to the sixth and 729 is 3 to the sixth. Only 1, 64 and 729 have the property below a thousand.
View 64 →Mathematically related
- is a multiple of64
why?
Strength 0.50, confidence "high".
Mathematics
A number that is both a square and a cube must be a sixth power, so below a thousand there are only 1, 64 and 729. The scarcity is why such numbers turn up as puzzle answers far more often than their frequency would suggest.
DocumentedMathematics
Common questions
Is 729 a prime number?
No, 729 is not prime.
What are the factors of 729?
The factors of 729 are 1, 3, 9, 27, 81, 243, 729.
What is 729 in Roman numerals?
729 in Roman numerals is DCCXXIX. IX is subtractive: one before ten — ten minus one. Written additively it would be DCCXXVIIII, 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