39
The Thirty-Nine Steps, John Buchan's 1915 thriller and Hitchcock's film of it, is what most people know 39 for. It is also the atomic number of yttrium, whose phosphors light most modern white LEDs.
- Odd
- Composite
Where 39 fits
Why 39 is special
39's cultural recognition comes almost entirely from Buchan's 1915 novel and Hitchcock's later film adaptation, not from any mathematical property.
Same number, different meanings
How 39 is understood across different contexts — never implying one meaning because of another.
- Mathematics
39's cultural recognition comes almost entirely from Buchan's 1915 novel and Hitchcock's later film adaptation, not from any mathematical property.
- Sport
In darts a player must finish on a double, so certain scores cannot end a leg. 39 is a standard 'bogey' checkout only in the sense of requiring a specific route; the genuinely impossible finishes above 158 are what players mean by unreachable.
- Media & popular culture
'The Thirty-Nine Steps' — John Buchan's 1915 novel, later a well-known Alfred Hitchcock film — gave its title number lasting recognition in British popular culture.
- Religion & belief
In Judaism, thirty-nine categories of work are prohibited on Shabbat. Enumerated in the Mishnah, tractate Shabbat, around 200 CE. The list is derived from the kinds of labour used in building the Tabernacle rather than from any general idea of effort, which is why it includes writing and kindling but not lifting something heavy. This is a scholarly account rather than the tradition's own framing.
- Science
39 is the atomic number of yttrium. Yttrium compounds are the phosphors behind the red in older colour televisions and are used in the white LEDs now lighting most homes.
39 is part of
Factors & digit properties
- Divisors (4)
- 1, 3, 13, 39
- Prime factorisation
- 3 × 13
- Digit sum
- 12
- Digital root
- 3
Representations
- Decimal
- 39
- Scientific notation
- 3.900 × 10^1
Roman numerals
X X X I X
XXXIX uses the subtractive pair IX: one before ten — ten minus one.
Binary
1 0 0 1 1 1
1 × 32 + 0 × 16 + 0 × 8 + 1 × 4 + 1 × 2 + 1 × 1 = 39
Octal
4 7
4 × 8 + 7 × 1 = 39
Hexadecimal
2 7
2 × 16 + 7 × 1 = 39
Read as powers of two: 32 + 4 + 2 + 1 = 39.
In historical numeral systems
Egyptian
3 hobbles, 9 strokes
3 × 10 + 9 × 1 = 39. The signs are simply repeated and added; where they sit on the line is a matter of layout, not value.
Babylonian
3 corner wedges + 9 vertical wedges
39 fits in a single sexagesimal place: 3 corner wedges + 9 vertical wedges.
Greek (Ionic)
lambda, then theta, marked as a numeral
lambda-theta + keraia
lambda + theta written in descending order and added — the letters carry their values wherever they stand, so this is addition, not place value.
Hebrew numerals
lamed, then tet
lamed-tet
lamed (30) + tet (9) = 39, written in descending order.
Chinese numerals
sān shí jiǔ
sān shí jiǔ
三 before 十 multiplies it: 3 tens. 九 after it adds 9. The written form mirrors the arithmetic — "sān shí jiǔ". The financial (anti-fraud) form is 參拾玖.
Maya
1 dot (upper, twenties place) over 3 bars + 4 dots (lower, units place)
1 × 20 + 19 = 39. 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
- Semiprime
Related numbers & connections
13 is a factor of 39 (13 × 3 = 39).
View 13 →39 appears in Numbers in culture and belief, the topic covering numbers that carry a documented cultural fact.
Sport
In darts a player must finish on a double, so certain scores cannot end a leg. 39 is a standard 'bogey' checkout only in the sense of requiring a specific route; the genuinely impossible finishes above 158 are what players mean by unreachable.
DocumentedSportGeography: darts as codified by the professional bodies
Media & popular culture
'The Thirty-Nine Steps' — John Buchan's 1915 novel, later a well-known Alfred Hitchcock film — gave its title number lasting recognition in British popular culture.
DocumentedMedia & popular culture
Mathematics
39 is the sum of five consecutive primes (3 + 5 + 7 + 11 + 13) and also the sum of the first three powers of three (3 + 9 + 27). Neither is a deep property, and having both at once is the kind of coincidence a small number can afford.
DocumentedMathematics
Religion & belief
In Judaism, thirty-nine categories of work are prohibited on Shabbat. Enumerated in the Mishnah, tractate Shabbat, around 200 CE. The list is derived from the kinds of labour used in building the Tabernacle rather than from any general idea of effort, which is why it includes writing and kindling but not lifting something heavy. This is a scholarly account rather than the tradition's own framing.
Tradition / practiceReligion & beliefCulture: JudaismPresented as belief or tradition, not as an established fact.
Science
39 is the atomic number of yttrium. Yttrium compounds are the phosphors behind the red in older colour televisions and are used in the white LEDs now lighting most homes.
DocumentedScience
Common questions
What are the 39 steps?
A set of stairs in John Buchan's 1915 thriller, at a house on the Kent coast, counted by the hero as a clue. Hitchcock's 1935 film changed the meaning entirely — there the Thirty-Nine Steps is the name of a spy ring — and the film's version is the one most people half-remember.
Is 39 a prime number?
No, 39 is not prime.
What are the factors of 39?
The factors of 39 are 1, 3, 13, 39.
What is 39 in Roman numerals?
39 in Roman numerals is XXXIX. IX is subtractive: one before ten — ten minus one. Written additively it would be XXXVIIII, 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: 5 reviewer-confirmed records, sourced and reviewed before publication.
Last reviewed: 15 July 2026