Let d(n) be defined as the sum of proper divisors of n (numbers less than n which divide evenly into n).
If d(a) = b and d(b) = a, where a ≠ b, then a and b are an amicable pair and each of a and b are called amicable numbers.
For example, the proper divisors of 220 are 1, 2, 4, 5, 10, 11, 20, 22, 44, 55 and 110; therefore d(220) = 284. The proper divisors of 284 are 1, 2, 4, 71 and 142; so d(284) = 220.
Evaluate the sum of all the amicable numbers under 10000.
[code=ruby]def d(n)
if n > 2
(1…(n-1)).select{|e| n % e == 0}.inject(:+)
else
1
end
end
p (4…10000).select {|a|
b = d(a)
a != b && d(b) == a
}.inject(:+)[/code]
mieli i mieli ale daje rade ;]
To ja przedstawię swój kod ;p Brzydki, nie rubyish-way ale działa zdecydowanie szybciej (przez zastosowanie tricku z sqrt) 
[code=ruby]#!/usr/bin/env ruby
class Fixnum
def divisiors
tab = Array.new
tab << 1
2.upto(Math.sqrt(self).floor) do |i|
if self % i == 0
tab << i
tab << self/i
end
end
tab.sort
end
end
def d(n)
n.divisiors.inject(:+)
end
puts (1…10000).select {|n|
b = d(n)
n != b && d(b) == n
}.inject(:+)[/code]