63
63 is one less than 64, which makes it the largest value six bits can hold — the same reason 255 and 65,535 recur in computing. It is also the atomic number of europium, the phosphor that gave colour television a usable red.
- Odd
- Composite
Where 63 fits
Why 63 is special
63 (7 × 9) is best understood by its neighbour: one less than 64, itself both a square and a binary power.
63 connects to:
- 9 — has factor
Same number, different meanings
How 63 is understood across different contexts — never implying one meaning because of another.
- Mathematics
63 (7 × 9) is best understood by its neighbour: one less than 64, itself both a square and a binary power.
- Technology & computing
Colour television had a red problem: early phosphors were dim, so sets were driven hard and the picture suffered. Europium-doped phosphors, adopted from the mid-1960s, emit a narrow, bright red and fixed it — element 63 is the reason colour CRTs became watchable, and europium phosphors carried through into compact fluorescent lamps and white LEDs. Europium compounds are also reported among the fluorescent security features of euro banknotes.
- Science
63 is the atomic number of europium. Its phosphors glow under ultraviolet light and are printed into euro banknotes as an anti-counterfeiting measure.
Factors & digit properties
- Divisors (6)
- 1, 3, 7, 9, 21, 63
- Prime factorisation
- 3^2 × 7
- Digit sum
- 9
- Digital root
- 9
Representations
- Decimal
- 63
- Scientific notation
- 6.300 × 10^1
Roman numerals
L X I I I
Binary
1 1 1 1 1 1
1 × 32 + 1 × 16 + 1 × 8 + 1 × 4 + 1 × 2 + 1 × 1 = 63
Octal
7 7
7 × 8 + 7 × 1 = 63
Hexadecimal
3 f
3 × 16 + f × 1 = 63
Read as powers of two: 32 + 16 + 8 + 4 + 2 + 1 = 63.
In historical numeral systems
Egyptian
6 hobbles, 3 strokes
6 × 10 + 3 × 1 = 63. The signs are simply repeated and added; where they sit on the line is a matter of layout, not value.
Babylonian
1 vertical wedge (sixties place), 3 vertical wedges (units place)
1 × 60 + 3 = 63. Places are separated by a space on the tablet, with the higher place written first.
Greek (Ionic)
xi, then gamma, marked as a numeral
xi-gamma + keraia
xi + gamma written in descending order and added — the letters carry their values wherever they stand, so this is addition, not place value.
Hebrew numerals
samekh, then gimel
samekh-gimel
samekh (60) + gimel (3) = 63, written in descending order.
Chinese numerals
liù shí sān
liù shí sān
六 before 十 multiplies it: 6 tens. 三 after it adds 3. The written form mirrors the arithmetic — "liù shí sān". The financial (anti-fraud) form is 陸拾參.
Maya
3 dots (upper, twenties place) over 3 dots (lower, units place)
3 × 20 + 3 = 63. 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
9 is a factor of 63 (9 × 7 = 63).
View 9 →Mathematically related
- has factor9
why?
Strength 0.50, confidence "high".
Technology & computing
Colour television had a red problem: early phosphors were dim, so sets were driven hard and the picture suffered. Europium-doped phosphors, adopted from the mid-1960s, emit a narrow, bright red and fixed it — element 63 is the reason colour CRTs became watchable, and europium phosphors carried through into compact fluorescent lamps and white LEDs. Europium compounds are also reported among the fluorescent security features of euro banknotes.
DocumentedTechnology & computingPeriod: mid-1960s – present
Science
63 is the atomic number of europium. Its phosphors glow under ultraviolet light and are printed into euro banknotes as an anti-counterfeiting measure.
DocumentedScience
Mathematics
63 = 7 × 9 = 7 × 3², sitting one below the power of two 64.
DocumentedMathematics
Common questions
Why does 63 keep appearing in computing?
Because it is 2⁶ − 1, so it is the largest value six bits can hold — the same way 255 is the largest for eight and 65,535 for sixteen. Whenever a limit is one short of a round binary number, that is what has happened.
Is 63 a prime number?
No, 63 is not prime.
What are the factors of 63?
The factors of 63 are 1, 3, 7, 9, 21, 63.
What is 63 in Roman numerals?
63 in Roman numerals is LXIII.
About this page's data
Mathematical facts:computed directly from the number's value — nothing to source or verify externally.
Contextual records: 3 reviewer-confirmed records, sourced and reviewed before publication.
Last reviewed: 15 July 2026