gistfile1.rb

def zipflaw(x, i)
  j = 0
  k = 1
  i.times do
    # I was stuck for awhile because I wasn't using floating points and the error was enough to move my answer back by 2 ranks!
    j += x.to_f/k.to_f
    k += 1
  end
  j
end

zipflaw(2520,900)
# => 18598.01801986991
zipflaw(2520,900) / 2
# => 9299.009009934955
zipflaw(2520,22)
# => 9300.849390547533
# close enough =)