Drexel dragonThe Math ForumDonate to the Math Forum

Ask Dr. Math - Questions and Answers from our Archives
_____________________________________________
Associated Topics || Dr. Math Home || Search Dr. Math
_____________________________________________

121, 111211, 311221 Puzzle (Look and Say Sequence)


Date: 10/23/2001 at 18:53:18
From: Joey
Subject: What's the next number?

121, 111211, 311221  - what's the next number?


Date: 10/23/2001 at 22:28:06
From: Doctor Paul
Subject: Re: What's the next number?

The first number is 121. If you were to describe this number to 
someone who was writing it down digit by digit, you would say:

Write down a single one - that is, one one. Then write down a single 
two - that is, one two. Finally, write down a single one - that is, 
one one.

Put them together: one one one two one one

Notice that this gives the next number:  111211

To describe this number in words digit by digit gives:

   three ones, one two, two ones = 311221

A similar pattern shows that the next numbers in the sequence are:

   13212211, 111312112221, 31131112213211

- Doctor Paul, The Math Forum
  http://mathforum.org/dr.math/   
    
Associated Topics:
High School Puzzles
High School Sequences, Series
Middle School Puzzles

Search the Dr. Math Library:


Find items containing (put spaces between keywords):
 
Click only once for faster results:

[ Choose "whole words" when searching for a word like age.]

all keywords, in any order at least one, that exact phrase
parts of words whole words

Submit your own question to Dr. Math

[Privacy Policy] [Terms of Use]

_____________________________________
Math Forum Home || Math Library || Quick Reference || Math Forum Search
_____________________________________

Ask Dr. MathTM
© 1994-2013 The Math Forum
http://mathforum.org/dr.math/