Number theory - prove if divisible by 2009

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SUMMARY

This discussion centers on proving the existence of an integer composed solely of the digits 0 and 1 that is divisible by 2009. The participant initially attempted to express the integer in the form of a polynomial equation involving powers of 10, but recognized the need for a different approach. The solution involves applying Dirichlet's box principle to the sequence of numbers formed by repeating the digit 1, demonstrating that two such numbers will eventually be congruent modulo 2009, leading to the desired integer.

PREREQUISITES
  • Understanding of number theory concepts, specifically divisibility.
  • Familiarity with Dirichlet's box principle.
  • Basic knowledge of modular arithmetic.
  • Ability to manipulate polynomial expressions involving powers of 10.
NEXT STEPS
  • Study the application of Dirichlet's box principle in number theory.
  • Learn about modular arithmetic and its properties.
  • Explore integer sequences and their properties in relation to divisibility.
  • Investigate other divisibility rules for composite numbers like 2009.
USEFUL FOR

This discussion is beneficial for students of number theory, mathematicians interested in divisibility problems, and educators looking for examples of applying principles like Dirichlet's box in problem-solving contexts.

DianaSagita
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Homework Statement



Prove if there exists an integer whose decimal notation contains only 0s and 1s, and which is divisible by 2009.


Homework Equations



Dirichlet's box principle :confused:

The Attempt at a Solution



I'm new to number theory, and I'm aware that I do not have the proper reasoning for this, but tried:
10^n + a[n-1]*10^(n-1) + ... + a[0] = k* (2*10^3 + 9), where a={0,1}

tried to find k with the max power of 10^(n-1), but it seems my approach is wrong... :( please help
Thanks in advance!
 
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Consider numbers of the form 1, 11, 111, 1111, ... According to the box principle at some point two members of this sequence will be equal modulo 2009. In that case subtract the smaller from the larger and you should get your integer.
 
Thank you, rasmhop! I understand now how to get it, your reply was helpful, cheers!
 

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