# 69 (number)
**69 (sixty-nine)** is the natural number following 68 and preceding 70. It is an odd composite number, specifically a [semiprime](https://www.edgepedia.org/semiprime), the product of exactly two primes, 3 and 23.[1](https://numbertrove.com/number/69/) Beyond arithmetic, the number is known as the atomic number of the rare earth element thulium and, in popular culture, as a slang reference to a sex position whose name dates to the 1880s.[2](https://periodic-table.rsc.org/element/69/thulium) • [3](https://www.etymonline.com/word/sixty-nine)
| Key fact | Detail |
|---|---|
| Factorization | 69 = 3 × 23, a semiprime with four divisors: 1, 3, 23, 69[1](https://numbertrove.com/number/69/) |
| Divisor sum | 96; the aliquot sum (proper divisors only) is 27[4](https://www.numberempire.com/69) |
| Square and cube | 69² = 4,761 and 69³ = 328,509; together they use each digit 0–9 exactly once[1](https://numbertrove.com/number/69/) |
| Factorial | 69! ≈ 1.7 × 10⁹⁸, the largest factorial below a googol (10¹⁰⁰)[1](https://numbertrove.com/number/69/) |
| Representations | Binary 1000101, octal 105, hexadecimal 45, Roman numeral LXIX[1](https://numbertrove.com/number/69/) |
| Chemistry | Atomic number of thulium (Tm), standard atomic weight 168.93[2](https://periodic-table.rsc.org/element/69/thulium) • [5](https://www.nist.gov/system/files/documents/2019/07/10/nist_periodictable_june_2019-crop.pdf) |
## Arithmetic properties
**Multiplicative structure.** Because 69 = 3 × 23, it has exactly four divisors, so it splits into equal whole-number groups in only two non-trivial ways.[1](https://numbertrove.com/number/69/) The sum of all divisors is 96, and since the sum of the proper divisors (1 + 3 + 23 = 27) is less than the number itself, 69 is a deficient number.[4](https://www.numberempire.com/69)
**Number-theory classifications.** It is also an Ulam number, an integer expressible as the sum of two distinct earlier Ulam numbers in the sequence that begins 1, 2; the (1, 2)-Ulam sequence indeed lists 69 among its terms.[6](https://oeis.org/wiki/Ulam_sequences) It does not belong to several classical special categories: it is not a perfect square, [Fibonacci](https://www.edgepedia.org/fibonacci) number, palindrome, [Armstrong number](https://www.edgepedia.org/narcissistic-number), or [Harshad number](https://www.edgepedia.org/harshad-number).[7](https://numbermath.com/number/69)
**Digit properties.** The digit sum of 69 is 15 and its digital root is 6; the digit-sum test explains why 69 is divisible by 3.[1](https://numbertrove.com/number/69/) • [7](https://numbermath.com/number/69) A distinctive property: in decimal, 69 is the only natural number whose square and cube together use every digit from 0 to 9 exactly once, since 69² = 4,761 and 69³ = 328,509.[1](https://numbertrove.com/number/69/) The number is also strobogrammatic: because a 6 turned upside down becomes a 9, 69 reads the same when rotated by a half-turn.[1](https://numbertrove.com/number/69/)
## The factorial boundary at 69
The factorial of 69 is approximately 1.7 × 10⁹⁸, while 70! exceeds 10¹⁰⁰ and overflows a two-digit exponent display.[1](https://numbertrove.com/number/69/) This makes 69 the largest whole number whose factorial is less than a googol, and it is the largest factorial that TI-83 series graphing calculators compute directly.[8](https://pjk.scripts.mit.edu/lab/mdm/McGraw-Hill_-_Data_Management_%28Text%29_Chapter_4.pdf) • [1](https://numbertrove.com/number/69/)
## Thulium, element 69
In chemistry, 69 is the atomic number of thulium (Tm), a soft, silvery rare earth metal sitting toward the end of the lanthanide series, the strip of elements between barium and lutetium.[2](https://periodic-table.rsc.org/element/69/thulium) NIST's periodic table lists its standard atomic weight as 168.93 and its ground-state electron configuration as [Xe]4f¹³6s².[5](https://www.nist.gov/system/files/documents/2019/07/10/nist_periodictable_june_2019-crop.pdf) Thulium is one of the rarest of the rare earths, and when irradiated in a nuclear reactor it produces an isotope that emits x-rays, used in lightweight portable x-ray machines for medical use; the element also serves in lasers with surgical applications.[2](https://periodic-table.rsc.org/element/69/thulium)
## Cultural associations
The number's best-known informal meaning comes from its shape. In the sexual sense, "sixty-nine" is attested from 1888 as a translation of the French *faire soixante neuf*, so called from the resemblance of two fitted partners to the arrangement of the numerals 6 and 9.[3](https://www.etymonline.com/word/sixty-nine) [Dictionary.com](https://www.edgepedia.org/dictionary-com) notes that English picked up the term by the 1880s, with the numerical shorthand 69 familiar by the 1970s.[9](https://www.dictionary.com/culture/slang/69) This association has made 69 a recurring internet meme, often greeted with the word "nice."[10](https://knowyourmeme.com/sensitive/memes/69-sixty-nine)
The year 1969 also fixed the number in popular memory: [Apollo 11](https://www.edgepedia.org/apollo-11) landed on the Moon that year, the [Woodstock](https://www.edgepedia.org/woodstock) festival drew hundreds of thousands to a New York dairy farm, and [Bryan Adams](https://www.edgepedia.org/bryan-adams) later sang about the "Summer of '69."[1](https://numbertrove.com/number/69/)
## Related sequences
The digits 69 appear in prime-hunting sequences. The OEIS entry A293001 collects numbers k such that 69 followed by k−1 zeros followed by 1 is prime; the first terms are 1, 3, 5, 15, 17, 37, 49, 80, 91, and 107, giving primes such as 691, 69001, and 6900001.[11](https://oeis.org/A293001) 69 also appears in the lucky numbers, the sieve-based sequence introduced by Stanislav Ulam, where it follows 67 and precedes 73.[12](https://research-solution.com/uplode/books/book-21764.pdf)
## References
1. [69: Number Facts, Factors & Representations, NumberTrove](https://numbertrove.com/number/69/)
2. [Thulium – Element information, properties and uses, Royal Society of Chemistry](https://periodic-table.rsc.org/element/69/thulium)
3. [Sixty-nine – Etymology, Origin & Meaning, Online Etymology Dictionary](https://www.etymonline.com/word/sixty-nine)
4. [Properties of the number 69, Number Empire](https://www.numberempire.com/69)
5. [Periodic Table – Atomic Properties of the Elements, NIST (June 2019)](https://www.nist.gov/system/files/documents/2019/07/10/nist_periodictable_june_2019-crop.pdf)
6. [Ulam sequences, OeisWiki](https://oeis.org/wiki/Ulam_sequences)
7. [Number 69 (sixty-nine) – Properties, Facts & Trivia, Math.Number](https://numbermath.com/number/69)
8. [McGraw-Hill Data Management, Chapter 4 (factorial on TI-83 calculators)](https://pjk.scripts.mit.edu/lab/mdm/McGraw-Hill_-_Data_Management_%28Text%29_Chapter_4.pdf)
9. [69 – Slang, Dictionary.com](https://www.dictionary.com/culture/slang/69)
10. [69 / Sixty-Nine, Know Your Meme](https://knowyourmeme.com/sensitive/memes/69-sixty-nine)
11. [A293001 – Numbers k such that 69*10^k + 1 is prime, OEIS](https://oeis.org/A293001)
12. [Figures in Mat (lucky numbers sequence)](https://research-solution.com/uplode/books/book-21764.pdf)
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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: Sep 30, 2026; Oct 15, 2026 · Edited: Oct 15, 2026; Oct 25, 2026 · Last review: Oct 15, 2026*
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