Palindrome numbers, and how many of them exist

    Tattarrattat, twelve letters, is the longest palindrome the Oxford English Dictionary holds. This tool checks any word, phrase or number for symmetry, names the exact position where it breaks, and draws examples from 66 verified palindromes.

    Palindrome numbers come from their own pool here, kept separate from the other three sets because somebody hunting a phrase for a crossword does not want three-letter first names. Every entry was verified by running it back through the checker on this page rather than by eye, which is not a formality: published palindrome lists routinely carry entries that fail once you strip the punctuation properly. Draws are random and without replacement, so asking twice gives a different selection, and asking for more than the pool holds returns the whole pool with a note saying so. The checker half of the tool is separate and works on anything at all, so if a candidate of your own is not on the list you can test it and see the exact position where the symmetry breaks.

    Parameters

    Enter data for calculations

    Test your own text, draw examples, or both

    The text to test for symmetry

    Between 1 and 20 per run

    Filters which set the examples come from

    Form progress0 / 1 fields

    💡 Fill in all required fields to unlock the calculate button

    Tattarrattat is twelve letters long and it is the longest palindrome in the Oxford English Dictionary

    James Joyce made the word up in Ulysses for the sound of a knock at a door, and it has been in the dictionary ever since. Everything shorter that people usually reach for sits well under half that length: racecar at seven, level at five, deed at four. This tool does two separate jobs. It takes anything you type, strips the capitals, spaces and punctuation, and tells you whether what is left is symmetrical, naming the exact position where it stops being symmetrical if it does. And it draws examples from 66 palindromes held in four sets, so you are not staring at a blank field trying to remember one.

    66
    palindromes on file, across four sets
    17,576
    five-letter palindrome patterns in a 26-letter alphabet
    12
    letters in tattarrattat, the dictionary record holder
    110
    years between the palindromic years 2002 and 2112

    From input to verdict, in five steps

    1. Mode - Check one tests what you type and nothing else. Draw examples ignores the text field entirely. Check one and draw examples does both in one run, which is the setting most people want.
    2. Word, phrase or number - anything goes in here. Capitals, spaces, commas and apostrophes are removed before the comparison, so Madam, I'm Adam is judged as the eleven characters madamimadam.
    3. How many examples - from 1 to 20. If the set you picked holds fewer than that, you get all of it and the output says so rather than handing back a short list without explanation.
    4. Which kind - single words, names and places, phrases and sentences, numbers, or all four mixed together. The filter exists because somebody hunting for a crossword phrase does not want three-letter first names.
    5. Read the verdict - a yes tells you how many character pairs matched. A no names the first position that broke and counts how many pairs disagree in total, so you can check the answer by hand instead of taking it on trust.

    What counts as the same backwards

    A palindrome is anything that reads identically in both directions, but almost every interesting example only qualifies after you agree to ignore some of what is written. A man, a plan, a canal, Panama has four commas and five spaces in it; drop them, drop the capitals, and 21 letters remain that mirror perfectly around the central c. Keep the punctuation and the same sentence fails on the first character. That convention is not a shortcut, it is the standard definition, and it is what this tool applies.

    Digits are kept for the same reason letters are. A checker that quietly drops them and then reports the input as too short is answering a question nobody asked, because 12321 is a palindrome under any definition anyone uses. Here a number is treated exactly like a word: 2002 passes, 2003 fails at the first position, and the readout tells you which position that was.

    What the tool will not do is invent a palindrome for you. There is no algorithm that produces Rats live on no evil star from nothing, because being a palindrome and being a sentence are two constraints that no generator satisfies at once by luck. What you get instead is a drawn sample from a list where every entry has been verified against the checker itself.

    How many palindromes could exist at each length

    Half of a palindrome fixes the other half, so the count of possible patterns depends only on the first half. For a 26-letter alphabet that gives 26 raised to the length rounded up and halved, which is why lengths five and six have exactly the same number of patterns. These are letter patterns, not words in any dictionary. Almost all of them are unpronounceable.

    Length Pattern Possible patterns Real example
    3 aba 676 Ada, Bob, Eve
    4 abba 676 noon, deed, sees
    5 abcba 17,576 level, radar, civic
    6 abccba 17,576 redder, Hannah
    7 abcdcba 456,976 racecar, deified, repaper
    11 6 free letters 308,915,776 detartrated, Wassamassaw
    12 6 free letters 308,915,776 tattarrattat

    What is in the four sets

    Set Entries Shortest Longest Use it for
    Single words 24 4 12 Spelling lessons, crossword fills
    Names and places 14 3 11 Naming a character, quiz rounds
    Phrases and sentences 16 11 51 Puzzle clues, epigraphs, party tricks
    Numbers 12 3 6 Test data, dates, maths classes

    Lengths in that table are counted after normalising, which is why the longest phrase reads as 51 characters even though it runs to sixty-nine with its spaces and full stops. Ask for twenty numbers and you will get twelve, because twelve is all there is.

    Six things worth knowing about palindromes

    The name is Greek and literal. Palin means again, dromos means running or way. A palindrome is a thing that runs back the way it came.
    The Sator Square beat everyone by two thousand years. SATOR AREPO TENET OPERA ROTAS is a five by five Latin word square that reads the same across, down, backwards and upwards. A copy was buried in the ash at Pompeii, so it was already old news before AD 79.
    Finnish holds the everyday record. Saippuakivikauppias, a seller of soapstone, runs to 19 letters and is an ordinary compound noun rather than a stunt.
    Palindromic years arrive in clumps and then vanish. After 1991 the next was 2002, eleven years later. The one after that is 2112, a gap of 110 years, because the century digits have to mirror the last two.
    02/02/2020 worked in every common date format. Day first, month first, backwards or forwards, it read the same. The previous date that managed all of those at once was 11/11/1111.
    In genetics the mirror is chemical, not alphabetical. GAATTC is called palindromic because reversing it gives CTTAAG, and swapping each base for its partner turns that back into GAATTC. It is the site the EcoRI enzyme cuts. Type GAATTC into this tool and it will correctly say no, because it compares letters and not base pairs.

    Who opens a tool like this

    Puzzle setters and crossword solvers need a phrase of a given length that survives being read backwards, and they need it now rather than after twenty minutes of staring. The phrase set exists for exactly that.

    Primary and secondary teachers use palindromes to teach letter order and symmetry, and the four sets let a lesson move from three-letter names up to a fifty-one character sentence without changing tools.

    Programmers write a palindrome check in their first week of any language and then need test cases for it: an even-length one, an odd-length one, a phrase with punctuation, a number, and something that fails at a known position. The verdict here names that position, so it doubles as an expected value.

    Writers and quiz hosts want the well-known ones spelled correctly, which is harder than it sounds when the sentence is fifty characters long and one dropped letter destroys it.

    Questions people ask

    Do spaces and punctuation count?
    No. They are stripped before the comparison, along with capital letters. That is the standard convention and it is the only one under which famous examples such as Was it a car or a cat I saw qualify at all. The output always prints the normalised string it actually compared, so you can see what was removed.
    Can a number be a palindrome?
    Yes, and this tool keeps digits rather than deleting them. 12321, 2002 and 123321 all pass. Mixed input works too, so a reference like A1 1A is compared as a11a and comes back as a palindrome.
    What is the longest palindrome in English?
    In the dictionary, tattarrattat at 12 letters, coined by James Joyce in Ulysses. Outside the dictionary, detartrated at 11 is the usual answer for a word with a technical meaning. Constructed sentences go far beyond both: people have built palindromes running to tens of thousands of letters, though they stop making sense long before that.
    Why does it say no for a word I was sure about?
    Read the position it names. The verdict tells you the first place where the character counting from the front stopped matching the one counting from the back, and how many pairs disagree in total. Nine times out of ten it is a doubled letter in the middle or a missing one near the end, and the two lines printed above the position, the normalised form and its reverse, make it obvious.
    Does the generator invent new palindromes?
    No, and no tool honestly can. Producing a string that mirrors itself is trivial, but producing one that is also a sentence in English is a search problem with almost no solutions, which is why the good ones are famous and have known authors. This generator draws from 66 checked entries. The checking half of the tool, by contrast, works on anything you type.
    Is a single letter a palindrome?
    By the strict definition yes, since there is nothing to contradict it, and mathematicians usually count the empty string too. This tool asks for at least 2 characters after normalising, because with one there is no pair to compare and a yes would tell you nothing. It says so rather than failing silently.
    Why do lengths five and six have the same number of patterns?
    Because only the first half is free. A five-letter palindrome is fixed by its first three characters and a six-letter one by its first three as well, the difference being that the five-letter version reuses its middle character instead of doubling it. Both come to 17,576, which is 26 cubed.

    Related tools

    Lorem Ipsum Generator

    Placeholder copy by the paragraph, sentence or word, for when the layout is ready and the text is not - Open the generator

    Barcode Generator

    Another string that has to satisfy a rule, except there the rule is a GS1 check digit - Open the generator

    Anagram Generator

    Rearranges the same letters instead of mirroring them, and counts how many arrangements exist - Open the generator

    Password Generator

    Strings built to have no pattern at all, which is the exact opposite requirement - Open the generator

    Random Number Generator

    Draws numbers from a range the way this one draws entries from a list - Open the generator

    See also

    Palindrome words - real examples, checked one by onePalindrome names - real examples, checked one by onePalindrome phrases - real examples, checked one by one

    Generator verified by the LiczGrupa.pl team

    Content, formulas and results have been reviewed for accuracy and relevance by our team of specialists.

    Krystian Szyszka

    Reviewed by: Krystian Szyszka

    Related topics

    palindrome generator
    palindrome checker
    is this word a palindrome
    what is a palindrome
    how to tell if a word is a palindrome
    longest palindrome in english
    palindrome words list
    palindrome phrases examples
    a man a plan a canal panama
    palindrome numbers like 12321
    palindrome names for characters
    tattarrattat meaning
    palindrome sentences for kids
    do spaces count in a palindrome
    palindrome test cases for coding