World’s longest palindrome?

"A man, a plan, a canoe, pasta, heros, rajahs, a coloratura, maps, snipe, percale, macaroni, a gag, a banana bag, a tan, a tag, a banana bag again (or a camel), a crepe, pins, Spam, a rut, a Rolo, cash, a jar, sore hats, a peon, a canal-- Panama!" - Guy Steele, CLTL2

See banana, banana, banana, banana, banana, banana, banana, banana, banana, banana, banana, banana, banana, banana, banana, banana, banana, banana, banana, banana, banana, banana, banana, banana, banana, banana, banana, banana, banana, banana, banana, banana, bees.<p>For any N &quot;See [banana,]* bees.&quot; can be longer than N.

&quot;Dammit, I&#x27;m mad...&quot; <a href="https:&#x2F;&#x2F;quotereference.wordpress.com&#x2F;2014&#x2F;12&#x2F;11&#x2F;dammit-im-mad&#x2F;" rel="nofollow">https:&#x2F;&#x2F;quotereference.wordpress.com&#x2F;2014&#x2F;12&#x2F;11&#x2F;dammit-im-ma...</a><p>PS I converted this into three palindromic tweets <a href="https:&#x2F;&#x2F;twitter.com&#x2F;sep332&#x2F;status&#x2F;928484353310711808" rel="nofollow">https:&#x2F;&#x2F;twitter.com&#x2F;sep332&#x2F;status&#x2F;928484353310711808</a>

How does this count as a palindrome? It&#x27;s just a bunch of nonsense words (ignoring all the acronyms, are the rest all actually even really words?) separated by commas, that doesn&#x27;t even seem to pretend to take on the structure of a sentence.<p>Am I misunderstanding the level of coherence of the text? If the requirements are that loose, it seems it would be trivial to generate a &#x27;palindrome&#x27; of arbitrary length.

I was recently dumbfounded by the fact that<p><pre><code> ()() </code></pre> is not a palindrome, but<p><pre><code> ())( </code></pre> is. It&#x27;s obvious, sure, but it still doesn&#x27;t look right.

The longest palindrome has infinite length. Start with any palindrome, e.g. &quot;radar&quot;. You can make a new palindrome: &quot;radar, sides reversed, is radar&quot;. That can then be used to create the palindrome &quot;radar, sides reversed, is radar, sides reversed, is radar, sides reversed, is radar&quot;.<p>You can repeat this indefinitely.

&quot;Never odd or even&quot; is one some here might like to see, and perhaps suggests the shorter palindrome, &quot;NaN&quot;.

World&#x27;s shortest palindrome:

There&#x27;s a link which takes you to the list of palindrome dates mentioned on the website [1]. There&#x27;s 38 of them, but they all take the MM&#x2F;DD&#x2F;YYYY format into consideration. I wonder how much of a difference it would be by taking DD&#x2F;MM&#x2F;YYYY instead.<p>[1] <a href="https:&#x2F;&#x2F;www.livescience.com&#x2F;33583-palindrome-dates-21st-century-weird.html" rel="nofollow">https:&#x2F;&#x2F;www.livescience.com&#x2F;33583-palindrome-dates-21st-cent...</a>

Different word trivia that I find fascinating that I feel HNers will also appreciate:<p>(twelve plus one) is an anagram of (eleven plus two)<p>I guess that should be called a mathagram?

I was a fan of this palindromic short story (also in honor of the year 2002): <a href="http:&#x2F;&#x2F;spinelessbooks.com&#x2F;2002&#x2F;palindrome&#x2F;" rel="nofollow">http:&#x2F;&#x2F;spinelessbooks.com&#x2F;2002&#x2F;palindrome&#x2F;</a>

Here&#x27;s a handcrafted one in Polish, 33K+ characters: <a href="http:&#x2F;&#x2F;www.palindromy.pl&#x2F;pal_naj.php" rel="nofollow">http:&#x2F;&#x2F;www.palindromy.pl&#x2F;pal_naj.php</a>

I&#x27;m also reminded of this IOCCC entry: <a href="https:&#x2F;&#x2F;www.ioccc.org&#x2F;1987&#x2F;westley&#x2F;westley.c" rel="nofollow">https:&#x2F;&#x2F;www.ioccc.org&#x2F;1987&#x2F;westley&#x2F;westley.c</a>. Strictly speaking, it&#x27;s not composed of palindromes because of the mirror-image brackets and slashes, but still, impressive.

I have to point out Weird Al&#x27;s &quot;Bob&quot;: <a href="https:&#x2F;&#x2F;www.youtube.com&#x2F;watch?v=JUQDzj6R3p4" rel="nofollow">https:&#x2F;&#x2F;www.youtube.com&#x2F;watch?v=JUQDzj6R3p4</a><p>It&#x27;s not a palindrome, but is a semi-sensical song masterfully composed entirely out of palindromes (which also does a great job poking fun at Bob Dylan).

This one is a valid sentence in Dutch:<p>&quot;Nelli plaatst op n parterretrap n pot staalpillen.&quot;<p>The &#x27;n&#x27;s are a bit of an issue though, &#x27;n in dutch means &#x27;een&#x27;, but reversed that doesn&#x27;t work so the &#x27;e&#x27;s got dropped and replaced by &quot;&#x27;&quot; but they move from one side of the n&#x27;s to the other in the reversal.

We used find the longest palindrome in a string as an interview question at Amazon back in 2004

Hug of death?

Georges Perec in 1969: <a href="http:&#x2F;&#x2F;homepage.urbanet.ch&#x2F;cruci.com&#x2F;lexique&#x2F;palindrome.htm" rel="nofollow">http:&#x2F;&#x2F;homepage.urbanet.ch&#x2F;cruci.com&#x2F;lexique&#x2F;palindrome.htm</a> (1247 words)

8102018 is not a palindromic because it isn&#x27;t a valid format date (it is, but is nonsense, so not valid on my standards :).<p>examples of valid date formats are: yyyy-mm-dd dd-mm-yyyy

engage le jeu que je le gagne

For single words, in Dutch there is:<p>koortsmeetsysteemstrook

Go hang a salami, I&#x27;m a lasagna hog.

I thought the point of palindromes were that they<p>1: Are the same forwards and backwards<p>2: Make coherent sense<p>Still pretty cool nonetheless, I suppose

This palindrome is surprisingly disappointing. Almost every word appears 100s of times...

My 2 &quot;go to&quot; palindromes...<p>I know a fat man called Ella C Namtafawnoki.<p>I got hang of fog nah togi.

Whats with Sadick? (15 times!). Also the F<i></i>*, C and S words!

For a line level palindrome homage to Douglas Hofstadter&#x27;s Crab Canon see<p><a href="https:&#x2F;&#x2F;juliagalef.com&#x2F;2017&#x2F;02&#x2F;21&#x2F;a-poem-for-douglas-hofstadter&#x2F;" rel="nofollow">https:&#x2F;&#x2F;juliagalef.com&#x2F;2017&#x2F;02&#x2F;21&#x2F;a-poem-for-douglas-hofstad...</a>

wo nemo toss a lasso to me now!

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