1

I'm stack at that question as I'm not sure which law does the sequence obey

What number comes next in this series: 1 11 21 1211 111221 312211 13112221:

  • 12113331
  • 1113213211
  • 13221113
  • 113211321
Community
  • 1
S.D.
  • 1,417
  • 2
    Look and say it. One one one three two one three two one one. – Daniel Fischer May 06 '14 at 08:27
  • 1
    http://en.wikipedia.org/wiki/Look-and-say_sequence – Mike May 06 '14 at 08:32
  • @DanielFischer: thanks, you can post it as an answer - I'll accept it. Sometimes I'm not sure whether such questions are indeed pointing on out-of-the-box thinking, or more on the knowledge of specific concepts. – S.D. May 06 '14 at 08:39

2 Answers2

3

The online encyclopedia of integer sequences (OEIS) can identify this sequence and much more. This is a mathematician's go-to resource for identifying sequences.

This particular sequence was invented by John Conway and has many interesting and surprisingly intricate properties, which you can read about here.

Caleb Stanford
  • 45,895
0

74.

or 513399018462776172772637.

or any other number.

The problem with these types of questions is that they hope you understand what rule they are trying to show without you understanding any of the other Turing machines producing a sequence with the exact same start. "Outside the box thinking" is exactly what this discourages.

No math question should ever be based on hope.

There are some interesting sequences that start that way. Studying them is certainly interesting. Guessing them is not so interesting.

ex0du5
  • 1,366
  • 8
  • 14
  • 1
    I fully disagree, the answer is: 42. Obviously. – Did May 06 '14 at 09:01
  • I completely second your point: you can simply justify any next number just using a polynomial of an appropriate degree would that be a mathematical problem. But then I came to a conclusion that it's not about only finding the correct answer, but finding the most probable one based on common sense etc. This is all subjective of course, but in some activities (especially related to working with other human beings) guessing what the question is about in the mind of those who asked it may be as important as finding the answer. – S.D. May 06 '14 at 09:20
  • @Did In one IQ test I've seen the task to continue the sequence: $$ 0,1,0,-1,\dots $$ I thought of $2$ or $0$ but now I see that obviously I missed the right answer $42$. – S.D. May 06 '14 at 09:20
  • @S.D. Let me rephrase your first comment above: "it" is not at all about "finding the correct answer" since there is no such thing as a correct answer. These tests are a fraud since they misuse the prestige of mathematics as an exact science to give an aura of scientificity to practices that have none. The not-so-funny aspect of the situation is that these have actual consequences on the real lives of real people... – Did May 06 '14 at 11:09