tag.rb

def f(n, seen)
	
	n1 = n
	while (n >= n1)
		
		if (!seen[n].nil?) then 
			raise if (n1 < seen[n])
		else
			seen[n] = n1
		end
		
		
		n = n * 3 + 1 if (n.odd?)
		n /= 2 while (n.even?)
	end
	
	
	
end


seen = {}

n = 3
2000.times \
{
	f(n, seen)
	n += 2
}

seen.to_a.each { |x, y| puts([x, y].join("\t")) }