Problem 346

346.rb

@@ -0,0 +1,23 @@
+require 'pp'
+
+ceiling = 10**12
+
+repunits = {}
+
+def find_repunit(number, base)
+  ((base**(number) - 1) / (base - 1))
+end
+
+2.upto(Math.sqrt(ceiling)) do |base|
+  counter = 2
+  loop do
+    repunit = find_repunit(counter, base)
+    break if repunit >= ceiling
+    if repunit-1 != base
+      repunits[repunit] = true
+    end
+    counter += 1
+  end
+end
+
+pp repunits.keys.inject(:+)+1