MathDB
Recurrence giving periods of rest before catching flies

Source: IMO ShortList 1999, combinatorics problem 3

November 14, 2004
combinatoricsIMO ShortlistRecurrenceSequencescounting

Problem Statement

A biologist watches a chameleon. The chameleon catches flies and rests after each catch. The biologist notices that: [*]the first fly is caught after a resting period of one minute; [*]the resting period before catching the 2mth2m^\text{th} fly is the same as the resting period before catching the mthm^\text{th} fly and one minute shorter than the resting period before catching the (2m+1)th(2m+1)^\text{th} fly; [*]when the chameleon stops resting, he catches a fly instantly.
[*]How many flies were caught by the chameleon before his first resting period of 99 minutes in a row? [*]After how many minutes will the chameleon catch his 98th98^\text{th} fly? [*]How many flies were caught by the chameleon after 1999 minutes have passed?