```Date: Jan 27, 1999 3:02 PM
Author: Helena Verrill
Subject: coins problem

a little while ago, someone asked the following:if you have 12 coins, one of which is eitherheavier or lighter than the others, the others allbeing the same weight, how can you determine whichone it it, and whether it's heavier or lighter, inthree weighings.Well, I did't think about this problem until lastweekend when I heard it for a second time.Anyway, it's not too hard to solve, but how aboutwhat is the minumum number of weighings that youneed to determine which is the odd one, and whetherit's heavy or light, from n coins?Eg, you can do 3 coins in 2 weighings,12 coins in 3, 38 coins in 4 weighings - I'd rather ask for what is the sequence a_nso that a_n is the maximum number of coins suchthat the odd one can be found (and said to be heavieror lighter).  I'd guess this starts 3,12,38...but I can't find this sequence in Sloanes integersequences, so presumably that means 38 is not themax you can do in 4 weighings... Anyone else tried?Helena
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