Number reference
39 explained.
39: thirty-nine, composite; factors, prime factorization, roots, binary, hexadecimal, and digit properties.
Identity and representations
- Written form
- thirty-nine
- Classification
- composite
- Factors
- 1, 3, 13, 39
- Prime factorization
- 3 × 13
- Square root
- 6.244998
- Cube root
- 3.391211
- Binary
- 100111
- Octal
- 47
- Hexadecimal
- 27
- Roman numeral
- XXXIX
- Digit sum
- 12
- Digital root
- 3
What makes 39 notable
- Semiprime. 39 = 3 × 13, a product of exactly two primes. That gives it just four divisors, so it splits into equal groups in only two non-trivial ways.
39 in everyday use
Thirty-nine is the atomic number of yttrium, a metal used in lasers and LED phosphors. John Buchan's thriller The Thirty-Nine Steps, filmed by Hitchcock in 1935, fixed the number in popular culture. The Protestant Old Testament has 39 books, and the Church of England's doctrine is summarised in its Thirty-Nine Articles of 1571. Queen's song "'39" appeared on A Night at the Opera in 1975, and The 39 Clues is a children's book series that began in 2008.
Thirty-nine is 3 × 13 and the sum of the first five odd primes, 3 + 5 + 7 + 11 + 13. It is the smallest number with multiplicative persistence 3: multiply its digits to get 27, again to get 14, and again to get 4 — three steps before reaching a single digit. In binary it is 100111, and its reversal, 93, is also three times a prime, 3 × 31.
Nearby numbers
How to read this page
The factor list shows every way 39 splits into equal whole-number groups — 4 divisors in total. The prime factorisation is the compact form of that same information, and the base conversions restate 39 for contexts that do not use decimal.
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