# 14 (number)
**14** (fourteen) is the natural number following 13 and preceding 15, the product of the primes 2 and 7. It is a composite, even, squarefree semiprime with four divisors, and it appears in number theory as the smallest even nontotient and the fourth [Catalan number](https://www.edgepedia.org/catalan-number).[9](https://r-knott.surrey.ac.uk/Fractions/fractions.html) In chemistry, 14 is the atomic number of silicon, and in everyday English it survives in the word *fortnight*, literally "fourteen nights".[1](https://primenumbers.info/14.htm) • [2](https://oeis.org/wiki/14) • [3](https://periodic-table.rsc.org/element/14/) • [4](https://www.etymonline.com/word/fortnight)
| Key fact | Detail |
|---|---|
| Arithmetic status | Composite and even; prime factorization 2 × 7; divisors 1, 2, 7, 14[1](https://primenumbers.info/14.htm) |
| Sequence membership | 5th semiprime (after 4, 6, 9, 10); 4th Catalan number (after 1, 2, 5); square pyramidal number[5](https://proofwiki.org/wiki/14) • [2](https://oeis.org/wiki/14) |
| Nontotient | Smallest even nontotient (the smallest nontotient is 3): no positive integer m satisfies φ(m) = 14, where φ is Euler's totient function[2](https://oeis.org/wiki/14) • [9](https://r-knott.surrey.ac.uk/Fractions/fractions.html) |
| Divisor-sum coincidence | σ₁(14) = 24 = σ₁(15), the first case of consecutive integers with equal divisor sums[5](https://proofwiki.org/wiki/14) |
| Chemistry | Atomic number 14 is silicon (Si), relative atomic mass 28.085, group 14, period 3[3](https://periodic-table.rsc.org/element/14/) |
| Language | *Fortnight* = a period of 14 days, from Old English *feowertyne niht*, "fourteen nights"[4](https://www.etymonline.com/word/fortnight) |
| Calendar | March 14 is celebrated as Pi Day, after the decimal expansion of π ≈ 3.14[6](https://time.com/4699479/pi-day-history-origins/) |
## Arithmetic properties
The number 14 factors uniquely as 2 × 7, so it has exactly four positive divisors: 1, 2, 7, and 14. Because it is a product of two distinct primes, it is a semiprime, the fifth one after 4, 6, 9, and 10.[1](https://primenumbers.info/14.htm) • [5](https://proofwiki.org/wiki/14) It is not a perfect square, and it is not a perfect number, since the sum of its proper divisors is 10 rather than 14.[1](https://primenumbers.info/14.htm)
Several small distinctions attach to 14 in number theory. It is the smallest even nontotient: [Euler's totient function](https://www.edgepedia.org/eulers-totient-function) φ(m), which counts integers up to m that are coprime to m, never takes the value 14.[2](https://oeis.org/wiki/14) • [9](https://r-knott.surrey.ac.uk/Fractions/fractions.html) It is also the first Keith number, a repfigit number named after Keith Keith, in which the digits 1 and 4 generate the number itself through a Fibonacci-like recurrence: 1, 4, 5, 9, 14.[5](https://proofwiki.org/wiki/14)
**Equal divisor sums.** The divisor sum function σ₁ adds up all positive divisors of a number. For 14 the sum is 1 + 2 + 7 + 14 = 24, and for its neighbor 15 it is 1 + 3 + 5 + 15 = 24 as well; 14 is the first positive integer sharing its divisor sum with its successor.[5](https://proofwiki.org/wiki/14) A related coincidence is that 14 × 15 = 210, the primorial 7#, the product of the primes up to 7.[5](https://proofwiki.org/wiki/14)
**Catalan and pyramidal appearances.** 14 is the fourth Catalan number, the sequence 1, 1, 2, 5, 14, 42, ... that counts many combinatorial structures, computed as \( \frac{1}{5}\binom{8}{4} = 14 \).[5](https://proofwiki.org/wiki/14) It is also a square pyramidal number, one of the integers 1, 5, 14, 30, 55, ... that count stacked squares.[2](https://oeis.org/wiki/14)
## Algebraic behavior
Factorization behaves differently in quadratic integer rings built on 14. In the ordinary integers, 14 is simply 2 × 7. In the ring \( \mathbb{Z}[\sqrt{14}] \), the element \( \sqrt{14} \) itself is composite, since \( (4-\sqrt{14})(7+2\sqrt{14}) = \sqrt{14} \); this ring is a unique factorization domain, with units of the form \( \pm(15+4\sqrt{14})^{n} \).[2](https://oeis.org/wiki/14) By contrast, \( \mathbb{Z}[\sqrt{-14}] \) is not a unique factorization domain and has class number 4, so some integers factor in more than one way there.[2](https://oeis.org/wiki/14)
A related open problem concerns the abundancy index. Two numbers are "friends" if they share the same ratio of divisor sum to the number itself; 14 has ratio \( 24/14 = 12/7 \). Whether 14 is solitary, meaning it has no friend other than itself, is unresolved. A 2025 arXiv note proves that any potential friend F of 14 must be an odd, non-square positive integer in which the prime 7 appears to an even exponent, that at most two prime divisors of F can have odd exponents, and that the primes 3 and 5 cannot both divide F.[7](https://arxiv.org/abs/2503.11694)
## 14 in chemistry
In the periodic table, atomic number 14 belongs to silicon (Si), a group 14, period 3 p-block element with electron configuration [Ne] 3s²3p² and [relative atomic mass](https://www.edgepedia.org/relative-atomic-mass) 28.085. Ultrapure silicon is a solid with a blue-gray metallic sheen, melting at 1414 °C and boiling at 3265 °C, with density 2.3296 g/cm³.[3](https://periodic-table.rsc.org/element/14/) Most silicon goes into alloys such as aluminum-silicon and ferro-silicon, used for dynamo and transformer plates, engine blocks, cylinder heads, and machine tools, and for deoxidizing steel.[3](https://periodic-table.rsc.org/element/14/) The coincidence that silicon sits in group 14 of the table gives the number a second, unrelated claim on the periodic table.
## Language and culture
The English word *fortnight* preserves 14 in daily speech. It is a seventeenth-century contraction of [Middle English](https://www.edgepedia.org/middle-english) *fourteniht*, from [Old English](https://www.edgepedia.org/old-english) *feowertyne niht*, literally "fourteen nights", reflecting an ancient Germanic custom of reckoning time by nights that Tacitus noted in *[Germania](https://www.edgepedia.org/germania-book)*.[4](https://www.etymonline.com/word/fortnight) A parallel word *sennight*, from "seven nights", once served for a week but has fallen out of use.[4](https://www.etymonline.com/word/fortnight)
The date March 14 gives the number a mathematical holiday. Because the date written 3/14 matches the opening digits of π, math enthusiasts celebrate [Pi Day](https://www.edgepedia.org/pi-day) on March 14; in 2009 the U.S. House of Representatives passed a resolution designating it National Pi Day to encourage schools to teach students about π.[6](https://time.com/4699479/pi-day-history-origins/)
In political history, the number names [Woodrow Wilson](https://www.edgepedia.org/woodrow-wilson)'s Fourteen Points, the principles the U.S. president drew up as a basis for ending World War I, presented to the German government in October 1918 and accepted by Germany on 23 October of that year.[8](https://mathshistory.st-andrews.ac.uk//Societies/IMU/)
## References
1. [Is number 14 a prime number? Factors and other properties of 14, primenumbers.info](https://primenumbers.info/14.htm)
2. [14, OeisWiki](https://oeis.org/wiki/14)
3. [Silicon, Element information, properties and uses, Royal Society of Chemistry](https://periodic-table.rsc.org/element/14/)
4. [Fortnight, Etymology, Origin & Meaning, Online Etymology Dictionary](https://www.etymonline.com/word/fortnight)
5. [14, ProofWiki](https://proofwiki.org/wiki/14)
6. [This Is How the Number 3.14 Got the Name 'Pi', Time](https://time.com/4699479/pi-day-history-origins/)
7. [Is 14 a Solitary Number?, arXiv:2503.11694](https://arxiv.org/abs/2503.11694)
8. [International Mathematical Union, MacTutor History of Mathematics](https://mathshistory.st-andrews.ac.uk//Societies/IMU/)
9. [Fractions and Decimals](https://r-knott.surrey.ac.uk/Fractions/fractions.html)
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*Topic: Encyclopedia › Physical world and mathematics › Mathematics and statistics › Numbers and algebra › Arithmetic and number systems › Integer sequences and partitions › Special and named integers › Named individual integers*
*Initially written Sep 17, 2026 · Reviewed: Oct 15, 2026 · Edited: Oct 15, 2026 · Last review: Oct 15, 2026*
*Copyright 2026 EdgeChat AI, a subsidiary of Biostate AI.*
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