399
399 BC is the year Socrates was executed.
- Odd
- Composite
Where 399 fits
Why 399 is special
He was convicted of impiety and corrupting the young, and could have gone into exile. Choosing to accept the sentence is the act that made him a philosophical figure rather than a defendant.
Factors & digit properties
- Divisors (8)
- 1, 3, 7, 19, 21, 57, 133, 399
- Prime factorisation
- 3 × 7 × 19
- Digit sum
- 21
- Digital root
- 3
Representations
- Decimal
- 399
- Scientific notation
- 3.990 × 10^2
Roman numerals
C C C X C I X
CCCXCIX uses the subtractive pair IX: one before ten — ten minus one.
Binary
1 1 0 0 0 1 1 1 1
1 × 256 + 1 × 128 + 0 × 64 + 0 × 32 + 0 × 16 + 1 × 8 + 1 × 4 + 1 × 2 + 1 × 1 = 399
Octal
6 1 7
6 × 64 + 1 × 8 + 7 × 1 = 399
Hexadecimal
1 8 f
1 × 256 + 8 × 16 + f × 1 = 399
Read as powers of two: 256 + 128 + 8 + 4 + 2 + 1 = 399.
In historical numeral systems
Egyptian
3 coils of rope, 9 hobbles, 9 strokes
3 × 100 + 9 × 10 + 9 × 1 = 399. The signs are simply repeated and added; where they sit on the line is a matter of layout, not value.
Babylonian
6 vertical wedges (sixties place), 3 corner wedges + 9 vertical wedges (units place)
6 × 60 + 39 = 399. Places are separated by a space on the tablet, with the higher place written first.
Greek (Ionic)
tau, then koppa, then theta, marked as a numeral
tau-koppa-theta + keraia
tau + koppa + theta written in descending order and added — the letters carry their values wherever they stand, so this is addition, not place value.
Hebrew numerals
shin, then tsadi, then tet
shin-tsadi-tet
shin (300) + tsadi (90) + tet (9) = 399, written in descending order.
Maya
3 bars + 4 dots (upper, twenties place) over 3 bars + 4 dots (lower, units place)
19 × 20 + 19 = 399. 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
- Harshad (Niven) number
- Lucky number (mathematical sieve)
Related numbers & connections
Socrates was executed in 399 BC and Alexander died in 323. Aristotle taught Alexander and had been taught by Plato, who was taught by Socrates — four generations linking a trial to an empire.
View 323 →Other connections
- is associated with323
why?
Strength 0.50, confidence "high".
History
Socrates was offered exile and declined it, arguing that a citizen who accepts a city's benefits cannot reject its judgements selectively. Everything known about him comes from students, chiefly Plato.
DocumentedHistoryGeography: AthensPeriod: 399 BC
Common questions
Is 399 a prime number?
No, 399 is not prime.
What are the factors of 399?
The factors of 399 are 1, 3, 7, 19, 21, 57, 133, 399.
What is 399 in Roman numerals?
399 in Roman numerals is CCCXCIX. IX is subtractive: one before ten — ten minus one. Written additively it would be CCCLXXXXVIIII, 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