Editing Palindrome (section)

== Types ==

=== Characters, words, or lines ===
{{seealso|Reversible poem}}
The most familiar palindromes in English are character-unit palindromes, where the characters read the same backward as forward. Examples are ''civic'', ''radar'', ''level'', ''rotor'', ''kayak'', ''madam'', and ''refer''. The longest common ones are ''rotator, deified, racecar'', and ''reviver''; longer examples such as ''redivider'', ''kinnikinnik'', and ''tattarrattat'' are orders of magnitude rarer.<ref>{{Cite web |url=https://books.google.com/ngrams/graph?content=kinnikinnik%2Ctattarrattat%2Crotator%2Cdeified%2Crepaper%2Creviver%2Credivider&year_start=1800&year_end=2019&corpus=26&smoothing=3 |title=Google nGrams frequencies |access-date=29 December 2022 |archive-date=29 December 2022 |archive-url=https://web.archive.org/web/20221229212046/https://books.google.com/ngrams/graph?content=kinnikinnik,tattarrattat,rotator,deified,repaper,reviver,redivider&year_start=1800&year_end=2019&corpus=26&smoothing=3 |url-status=live }}</ref><!-- per {{WP:INDISCRIMINATE}}, please don't add further examples just because you can; these are EXAMPLES only -->

There are also word-unit palindromes in which the unit of reversal is the word ("Is it crazy how saying sentences backwards creates backwards sentences saying how crazy it is?"). Word-unit palindromes were made popular in the [[Logology (linguistics)|recreational linguistics]] community by [[J. A. Lindon]] in the 1960s. Occasional examples in English were created in the 19th century. Several in French and Latin date to the [[Middle Ages]].<ref>{{cite web
 |url          = http://www.kmjn.org/notes/word_unit_palindromes.html
 |title        = Word-unit palindromes
 |author       = Mark J. Nelson
 |date         = 7 February 2012
 |access-date  = 18 November 2012
 |archive-date = 12 February 2013
 |archive-url  = https://web.archive.org/web/20130212034438/http://www.kmjn.org/notes/word_unit_palindromes.html
 |url-status   = live
}}</ref>

There are also line-unit palindromes, most often [[Palindrome poem|poems]]. These possess an initial set of lines which, precisely halfway through, is repeated in reverse order, without alteration to word order within each line, and in a way that the second half continues the "story" related in the first half in a way that makes sense, this last being key.<ref>"Never Odd Or Even, and Other Tricks Words Can Do" by O.V. Michaelsen (Sterling Publishing Company: New York), 2005 p124-7</ref>

{| class="wikitable"
|+
Example
!Initial order
!Reversed order
|-
|{{color|crimson|We can save the world}}<br>I cannot believe that<br>{{color|navy|The world is doomed}}
|{{color|navy|The world is doomed}}<br>I cannot believe that<br>{{color|crimson|We can save the world}}
|}

=== Sentences and phrases ===
{{Main list|List of English palindromic phrases}}
[[File:Ambigram_Dogma_I_am_god.png|thumb|[[Ambigram]] of the palindrome "Dogma I am God"]]
Palindromes often consist of a sentence or phrase, e.g., "A man, a plan, a canal, Panama", "Mr. Owl ate my metal worm", 
"Do geese see God?", or "Was it a car or a cat I saw?". Punctuation, capitalization, and spaces are usually ignored. Some, such as "Rats live on no evil star", "Live on time, emit no evil", and "Step on no pets", include the spaces.

=== Names ===
Some names are palindromes, such as the [[given name]]s Hannah, Ava, Aviva, Anna, Eve, Bob, and Otto, or the [[surname]]s Harrah, Renner, Salas, and Nenonen.
[[Lon Nol]] (1913–1985) was Prime Minister of Cambodia. [[Nisio Isin]] is a Japanese novelist and [[manga]] writer, whose pseudonym (西尾 維新, ''Nishio Ishin'') is a palindrome when romanized using the [[Kunrei-shiki]] or the [[Nihon-shiki]] systems, and is often written as NisiOisiN to emphasize this. Some people have changed their name in order to make it palindromic (including as the actor [[Robert Trebor]] and rock-vocalist [[Ola Salo]]), while others were given a palindromic name at birth (such as the philologist [[Revilo P. Oliver]], the flamenco dancer [[Sara Baras]], the runner [[Anuța Cătună]], the creator of the [[Eden Project]] [[Tim Smit]], and the Mexican racing driver [[Noel León]]).
Savas (Emil M. Savas) Painter from [[Denmark]] christened with the palindrome Savas. The family name is of [[Kurdistan|Kurdish]] origin and derived from Savaş written with Ş /ʃ/ ([[Kurdish alphabets|Hawar alphabet]], [[Celadet Alî Bedirxan|Bedirxan 1932]]). The spelling was changed in accordance with the [[Danish and Norwegian alphabet|Dano-Norwegian alphabet]] when Savas’ father was granted danish citizenship.

There are also palindromic names in fictional media. "Stanley Yelnats" is the name of the main character in ''[[Holes (novel)|Holes]]'', a 1998 novel and [[Holes (film)|2003 film]]. Five of the fictional ''[[Pokémon]]'' [[List of Pokémon|species]] have palindromic names in English ([[Eevee]], Girafarig, Farigiraf, Ho-Oh, and Alomomola), as does the region Alola.

The 1970s pop band [[ABBA]] is a palindrome using the starting letter of the first name of each of the four band members.

=== Numbers ===
{{Main|Palindromic number}} {{Main|Periodic continued fraction}}
[[File:Immatriculation palyndromique.jpg|thumb|Palindromic license plate number]]

The digits of a palindromic number are the same read backwards as forwards, for example, 91019; [[decimal]] representation is usually assumed. In [[recreational mathematics]], palindromic numbers with special properties are sought. For example, 191 and 313 are [[palindromic prime]]s.

Whether [[Lychrel number]]s exist is an unsolved problem in mathematics about whether all numbers become palindromes when they are continuously reversed and added. For example, 56 is not a Lychrel number as 56 + 65 = 121, and 121 is a palindrome. The number 59 becomes a palindrome after three iterations: 59 + 95 = 154; 154 + 451 = 605; 605 + 506 = 1111, so 59 is not a Lychrel number either. Numbers such as 196 are thought to never become palindromes when this reversal process is carried out and are therefore suspected of being Lychrel numbers. If a number is not a Lychrel number, it is called a "delayed palindrome" (56 has a delay of 1 and 59 has a delay of 3). In January 2017 the number 1,999,291,987,030,606,810 was published in OEIS as [[oeis:A281509|A281509]], and described as "The Largest Known Most Delayed Palindrome", with a delay of 261. Several smaller 261-delay palindromes were published separately as [[oeis:A281508|A281508]].

Every positive integer can be written as the sum of three palindromic numbers in every number system with base 5 or greater.<ref>{{cite arXiv|last1=Cilleruelo|first1=Javier|last2=Luca|first2=Florian|last3=Baxter|first3=Lewis|date=19 February 2016|title=Every positive integer is a sum of three palindromes|eprint=1602.06208|class=math.NT}}</ref>

=== Dates ===
A day or timestamp is a palindrome when its digits are the same when reversed. Only the digits are considered in this determination and the component separators (hyphens, slashes, and dots) are ignored. Short digits may be used as in ''[[11/11/11]] 11:11'' or long digits as in ''2 February 2020''.

A notable palindrome day is this century's 2 February 2020 because this date is a palindrome regardless of the [[date format by country]] (yyyy-mm-dd, dd-mm-yyyy, or mm-dd-yyyy) used in various countries. For this reason, this date has also been termed as a "Universal Palindrome Day".<ref>{{cite web |display-authors= 0 |first= Susam |last= Pal |url= https://susam.in/blog/universal-palindrome-day/ |title= Universal Palindrome Day |date= 2 February 2020 |access-date= 3 February 2020 |archive-date= 6 August 2020 |archive-url= https://web.archive.org/web/20200806042809/https://susam.in/blog/universal-palindrome-day/ |url-status= dead }}</ref><ref>{{cite web |url= https://www.bbc.com/news/world-51349158 |title= #PalindromeDay: Geeks around the world celebrate 02/02/2020 |publisher= BBC |date= 2 February 2020 |access-date= 2 February 2020 |archive-date= 2 February 2020 |archive-url= https://web.archive.org/web/20200202183440/https://www.bbc.com/news/world-51349158 |url-status= live }}</ref> Other universal palindrome days include, almost a millennium previously, ''11/11/1111'', the future ''12/12/2121'', and in a millennium ''03/03/3030''.<ref>{{cite web |url= https://www.npr.org/2020/02/02/802015917/why-a-day-like-sunday-hasnt-been-seen-in-900-years |title= Why A Day Like Sunday Hasn't Been Seen In 900 Years |publisher= NPR |date= 2 February 2020 |first= Amy |last= Held |access-date= 3 February 2020 |archive-date= 3 February 2020 |archive-url= https://web.archive.org/web/20200203154420/https://www.npr.org/2020/02/02/802015917/why-a-day-like-sunday-hasnt-been-seen-in-900-years |url-status= live }}</ref>

=== {{anchor|Phonetic}} In speech ===
{{Listen|filename=uneslavevalsenue.ogg|title="Une Slave valse nue" played forward and backward}}
A phonetic palindrome is a portion of [[Speech communication|speech]] that is identical or roughly identical when reversed. It can arise in context where language is played with, for example in slang dialects like ''[[verlan]]''.<ref>{{cite journal
  | last1   = Goertz
  | first1  = Karein K.
  | title   = Showing Her Colors: An Afro-German Writes the Blues in Black and White
  | journal = Callaloo
  | date    = 2003
  | volume  = 26
  | issue   = 2
  | pages   = 306–319
  | doi     = 10.1353/cal.2003.0045
  | jstor   = 3300855
| s2cid = 161346520
 }}</ref> In the [[French language]], there is the phrase ''{{wikt-lang|fr|une Slave valse nue}}'' ("a Slavic woman waltzes naked"), phonemically {{IPA|{{nowrap|/[[Help:IPA/French|yn slav vals ny]]/}}}}.<ref>{{cite book
  | last1     = Durand
  | first1    = Gerard
  | title     = Palindromes en Folie
  | date      = 2003
  | publisher = Les Dossiers de l'Aquitaine
  | isbn      = 978-2846220361
  | page      = 32
  | url       = https://books.google.com/books?id=PK_xfgb1VQYC&pg=PA32
}}</ref>  [[John Oswald (composer)|John Oswald]] discussed his experience of phonetic palindromes while working on audio tape versions of the [[cut-up technique]] using recorded readings by [[William S. Burroughs]].<ref>{{cite web
  | url        = http://www.pfony.com/
  | title        = Section titled "On Burroughs and Burrows ..."
  | publisher        = Pfony.com
  | access-date        = 23 April 2012
  | archive-date        = 5 February 2012
  | archive-url        = https://web.archive.org/web/20120205201727/http://www.pfony.com/
  | url-status        = live
  }}</ref><ref>[http://www.pfony.com/burrows/index.html Reversible audio cut-ups of William S. Burroughs' voice] {{Webarchive|url=https://web.archive.org/web/20080313101733/http://www.pfony.com/burrows/index.html |date=13 March 2008 }}, including an acoustic palindrome in example 5 (requires [[Adobe Flash|Flash]])</ref>  A list of phonetic palindromes discussed by [[word puzzle]] columnist O.V. Michaelsen (Ove Ofteness) include "crew work"/"work crew", "dry yard", "easy", "Funny enough", "Let Bob tell", "new moon", "selfless", "Sorry, Ross", "Talk, Scott", "to boot", "top spot" (also an orthographic palindrome), "Y'all lie", "You're caught. Talk, Roy", and "You're damn mad, Roy".<ref>{{cite book
  | last1     = Michaelsen
  | first1    = O.V.
  | title     = Words at play: quips, quirks and oddities
  | date      = 1998
  | publisher = Sterling
}}</ref>