adds two more solutions

euler.rb

@@ -4,6 +4,20 @@ class Integer
   def to_digit_list
     self.to_s.split('').map(&:to_i)
   end
+
+  def factorial
+    i = 1
+    n = self
+    while (n > 0)
+      i *= n
+      n -= 1
+    end
+    i
+  end
+
+  def choose(k)
+    factorial / (k.factorial * (self - k).factorial)
+  end
 end
 
 module Euler

euler053.rb

@@ -0,0 +1,11 @@
+require_relative 'euler'
+
+def solution
+  result = 0
+  (1..100).each do |n|
+    (1..n).each do |k|
+      result += 1 if n.choose(k) > 1000000
+    end
+  end
+  result
+end

euler055.rb

@@ -0,0 +1,17 @@
+require_relative 'euler'
+
+def reverse_and_add(n)
+  n + Euler.from_digit_list(n.to_digit_list.reverse)
+end
+
+def lychrel_number?(n)
+  50.times do
+    n = reverse_and_add(n)
+    return false if Euler.palindrome?(n)
+  end
+  true
+end
+
+def solution
+  (1..10000).count { |x| lychrel_number?(x) }
+end