Integer#gnomonic?: Add

lib/numb/gnomonic.rb

@@ -0,0 +1,4 @@
+# coding: utf-8
+class Integer
+  alias :gnomonic? :odd?
+end

spec/numb/gnomonic_spec.rb

@@ -0,0 +1,21 @@
+# coding: utf-8
+describe Integer, "#gnomonic?" do
+  # A005408
+  @seq = [1,3,5,7,9,11,13,15,17,19,21,23,25,27,29,31,33,35,
+          37,39,41,43,45,47,49,51,53,55,57,59,61,63,65,67,
+          69,71,73,75,77,79,81,83,85,87,89,91,93,95,97,99,
+          101,103,105,107,109,111,113,115,117,119,121,123,
+          125,127,129,131]
+
+  @seq.each do |n|
+    it "returns true for gnomonic number #{n}" do
+      n.should be_gnomonic
+    end
+  end
+
+  @seq.to_seq.invert.each do |n|
+    it "returns false for non-gnomonic number #{n}" do
+      n.should_not be_gnomonic
+    end
+  end
+end