Difference between revisions of "2021 OIM Problems/Problem 3"

(Created page with "== Problem == Let <math>a_1, a_2, a_3, \cdots</math> be a sequence of positive integers and let <math>b_1, b_2, b_3, \cdots</math> be the sequence of real numbers given by <...")
 
 
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Let <math>a_1, a_2, a_3, \cdots</math> be a sequence of positive integers and let <math>b_1, b_2, b_3, \cdots</math> be the sequence of real numbers given by
 
Let <math>a_1, a_2, a_3, \cdots</math> be a sequence of positive integers and let <math>b_1, b_2, b_3, \cdots</math> be the sequence of real numbers given by
  
<math></math>b_n=\frac{a_1a_2,\cdots a_n}{a_1+a_2+\cdots + a_n}, \text{ for } n \ge 1.
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<cmath>b_n=\frac{a_1a_2,\cdots a_n}{a_1+a_2+\cdots + a_n}, \text{ for } n \ge 1.</cmath>
  
 
Show that if among every one million consecutive terms of the sequence <math>b_1, b_2, b_3, \cdots</math> there is at least one integer, then there is some <math>k</math> such that <math>b_k > 2021^{2021}</math>.
 
Show that if among every one million consecutive terms of the sequence <math>b_1, b_2, b_3, \cdots</math> there is at least one integer, then there is some <math>k</math> such that <math>b_k > 2021^{2021}</math>.

Latest revision as of 02:57, 14 December 2023

Problem

Let $a_1, a_2, a_3, \cdots$ be a sequence of positive integers and let $b_1, b_2, b_3, \cdots$ be the sequence of real numbers given by

\[b_n=\frac{a_1a_2,\cdots a_n}{a_1+a_2+\cdots + a_n}, \text{ for } n \ge 1.\]

Show that if among every one million consecutive terms of the sequence $b_1, b_2, b_3, \cdots$ there is at least one integer, then there is some $k$ such that $b_k > 2021^{2021}$.

Solution

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See also

https://olcoma.ac.cr/internacional/oim-2021/examenes