uglier is sometimes faster

not_ugly_test.rb

#!/usr/bin/env ruby

require 'yaml'

y=[]
(1..10000).each{|x|
  #next unless x/2==(1.0*x)/2
  z=x
  divisors=[1]
  _continue=true
  while _continue
    _continue=false
    ((divisors.last+1)..z).each{|w|
      r=z/w
      if (1.0*z)/w==r && w<x
        divisors<<w
        _continue=true
        break
      end
    }
  end
  if divisors.inject(&:+)>x and (3..(divisors.count)).find{|w| divisors.combination(w).find{|w2| w2.inject(&:+)==x } }
    y<<x
  end
}
puts "amount: #{y.count}"

ugly_test.rb

#!/usr/bin/env ruby

require 'yaml'

class Test
  attr_reader :y
  def initialize(up)
    @up = up
    @y = []
  end
  def perform
    for x in 1..@up
      divisors, w = [1], 1
      while (w = get_next(w+1, x))
        divisors << w
      end
      y << x if sum(divisors) > x && check(divisors, x)
    end
    self
  end
  def get_next(from, z)
    w = from
    while w < z
      return w if z/w == (1.0*z)/w
      w += 1
    end
    nil
  end
  def sum(ar)
    s = ar[0]
    i, up = 1, ar.size
    while i < up
      s += ar[i]
      i += 1
    end
    s
  end
  def check(divisors, x)
    (3..(divisors.count)).find{|w|
      divisors.combination(w).find{|w2|
        sum(w2) == x
      }
    }
  end
end
puts "amount: #{Test.new(10000).perform.y.count}"

In JRuby, #[] is flagged as a method that requires a heap-based scope because some versions of it set $~ (backref). Using .at avoids that.

Wow :)

@mpapis that certainly could be true. There's also been some optimization work on JRuby master that may not be in your copy.