Editing 169 (number)

{{Infobox number
| number = 169
| divisor=1, 13, 169
}}

'''169''' ('''one hundred [and] sixty-nine''') is the natural number following [[168 (number)|168]] and preceding [[170 (number)|170]].
==In mathematics==
169 is an [[odd number]], a [[composite number]], and a [[deficient number]].

169 is a [[square number]]: [[13 (number)|13]] × 13 = 169, and if each number is reversed the equation is still true: [[31 (number)|31]] × [[31 (number)|31]] = 961. [[144 (number)|144]] shares this property: 12 × 12 = 144, 21 × 21 = 441.

169 is one of the few squares to also be a [[centered hexagonal number]].<ref>{{Cite web|url=https://oeis.org/A003215|title=Sloane's A003215 : Hex (or centered hexagonal) numbers|website=The On-Line Encyclopedia of Integer Sequences|publisher=OEIS Foundation|access-date=2016-05-28}}</ref> Like all odd squares, it is a [[centered octagonal number]]. 169 is an odd-indexed [[Pell number]], thus it is also a [[Markov number]], appearing in the solutions (2, 169, 985), (2, 29, 169), (29, 169, 14701), etc. 169 is the sum of seven consecutive [[prime number|prime]]s: [[13 (number)|13]] + [[17 (number)|17]] + [[19 (number)|19]] + [[23 (number)|23]] + [[29 (number)|29]] + [[31 (number)|31]]  + [[37 (number)|37]]. 169 is a difference in consecutive cubes, equaling <math>8^3-7^3.</math>

==In other fields==
* 169 is known in the [[computer|computing]] world as the first number of an [[IP address#Address autoconfiguration|automatic IPv4 address]] assigned by [[TCP/IP]] when no external [[Computer network|networking]] device is contactable

== References ==
{{Reflist}}
==External links==
{{Commons category}}
* [https://web.archive.org/web/20100123001222/http://athensohio.net/reference/number/169/ Number Facts and Trivia: 169]
* [http://www.positiveintegers.org/169 The Positive Integer 169]
* [https://t5k.org/curios/page.php/169.html Prime curiosities: 169]
* [https://web.archive.org/web/20160307161301/http://numdic.com/169 The Number 169]
* [http://www.numbergossip.com/169 Number Gossip 169]
{{Integers|1}}

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[[Category:Integers]]