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by LeMeThink on February 20th, 2007

LeMeThink

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What is the next number in this series: 1, 11, 21, 1211, 111221,......?

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Answers. 14 helpful answers below.

  • by Box of Chocolates on February 20th, 2007

    Box of Chocolates

    111221 is three ones, two two's, and one one.
    The next number is 312211.

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  • by Kevisaurus is a Carnotaurus today on June 26th, 2008

    Kevisaurus is a Carnotaurus today

    1113213211

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  • by rock on June 26th, 2008

    rock

    dgjlskmgdmsklblzdkglkag

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  • by bwright on June 4th, 2008

    bwright

    1113213211

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  • by xprofessor on February 28th, 2008

    xprofessor

    This is a well known sequence, known as a "look and say" sequence where each term describes the previous term. It uses a form of run-length encoding.

    Given an initial term of 1, the next term describes it as "one 1" = 11 (which is two 1's)
    Now each new term will describe the previous term.
    "two 1's" = 21
    "one 2, one 1" = 1211
    "one 1, one 2, two 1's" = 111221
    "three 1's, two 2's, one 1" = 312211
    etc., growing in length.

    It has been proven that the sequence contains only the digits 1, 2, and 3.

    Reference: http://www.research.att.com/~njas/sequences/A005150

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  • by Quirkie on January 27th, 2008

    Quirkie

    The first number has one '1'. Write that 11.
    The second number has 2 '1's. Write that 21.
    The third number has 1 2, and 1 1: 1211
    The fourth number has 1 1, 1 2 and 2 1s : 111221
    The fifth number: 31,22,11
    The sixth number: 13,11,22,21
    The seventh number: 11,13,21,32,11

    So the answer is 1113213211

    which is interestingly different from the other two answers so far.

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  • by -O-uknow on January 26th, 2008

    -O-uknow

    4122

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  • by onemill555 on August 10th, 2008

    onemill555

    123456789 123456789 2345467889 3456789
    How about what ever series of numbers I am feeling at the time?
    That's MY
    "Out of the box answer."

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  • by Kyogre-Stataen on August 20th, 2007

    Kyogre-Stataen

    113112221

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  • by Lara_S on February 24th, 2011

    Lara_S

    13211311123113112211

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  • by -O-uknow on January 26th, 2008

    -O-uknow

    411332

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  • by Nick Lalo on August 10th, 2008

    Nick Lalo

    the first number is a 1(one). The second number describes the first number. There is one one. So 11. the next one describes the one before it. There are two ones. 21. The third number describes the second number. one two and one one. Giving you 1211. It just keeps going up from there. I hope i explained that well enough for you with my bad english skills.

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  • by JohnOBonno on August 10th, 2008

    JohnOBonno

    2

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  • by ecarrion on May 18th, 2010

    ecarrion

    gj

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More Questions. Additional questions in this category.

You're reading What is the next number in this series: 1, 11, 21, 1211, 111221,......? - which can also be phrased in the following ways:

  • What is the next line in the sequence 1 11 21 1211 111221 312211 13112221
  • What comes next: 1, 11, 21, 1211, 111221, 312211, 13112221...

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