Proving Fibonacci Number as Permutations with Restriction |p(k)-k| \leq 1

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SUMMARY

The discussion focuses on proving that the number of permutations p on the set {1,2,3,...,n} with the condition |p(k)-k| ≤ 1 for all 1 ≤ k ≤ n corresponds to the Fibonacci number f_n. Participants clarify the definition of permutations and explore the constraints imposed by the condition, leading to a structured approach for constructing valid permutations. The relationship between the permutations and Fibonacci numbers is established through recursive reasoning.

PREREQUISITES
  • Understanding of permutations and their properties
  • Familiarity with Fibonacci numbers and their recursive definitions
  • Basic knowledge of mathematical proofs and induction
  • Ability to analyze constraints in combinatorial problems
NEXT STEPS
  • Study the recursive definition of Fibonacci numbers and their applications
  • Learn about combinatorial proofs and techniques
  • Explore the concept of restricted permutations in combinatorics
  • Investigate the relationship between permutations and other number sequences
USEFUL FOR

Mathematics students, combinatorial theorists, and anyone interested in the intersection of permutations and Fibonacci numbers.

alec_tronn
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Homework Statement


Prove that the number of permutations p on the set {1,2,3,...,n} with the property that |p(k)-k| \leq 1, for all 1\leqk\leqn, is the fibonacci number f_{n}


The Attempt at a Solution


I guess I don't understand what it's asking. I thought I knew what a permutation was... but now I'm really confused. Can someone please restate this problem in a way that maybe I could understand? Thanks a lot!
 
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Consider constructing one of those permutations, to pick the first number I need to satisfy |p(1)-1|<=1. So p(1) can only be 1 or 2. Similarly p(2) can only be 1,2 or 3. p(3) can be 2,3 or 4. Etc.
 

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