Perfect totient numbers: Difference between revisions

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 The first 20 perfect totient numbers are:
 [3, 9, 15, 27, 39, 81, 111, 183, 243, 255, 327, 363, 471, 729, 2187, 2199, 3063, 4359, 4375, 5571]
+</pre>
+=={{header|Lua}}==
+<lang Lua>local function phi(n)
+   assert(type(n) == 'number', 'n must be a number!')
+   local result, i = n, 2
+   while i <= n do
+      if n % i == 0 then
+	 while n % i == 0 do n = n // i end
+	 result = result - (result // i)
+      end
+      if i == 2 then i = 1 end
+      i = i + 2
+   end
+   if n > 1 then result = result - (result // n) end
+   return result
+end
+local function phi_iter(n)
+   assert(type(n) == 'number', 'n must be a number!')
+   if n == 2 then
+      return phi(n) + 0
+   else
+      return phi(n) + phi_iter(phi(n))
+   end
+end
+local i, count = 2, 0
+while count ~= 20 do
+   if i == phi_iter(i) then
+      io.write(i, ' ')
+      count = count + 1
+   end
+   i = i + 1
+end
+</lang>
+{{output}}
+<pre>
+9 15 27 39 81 111 183 243 255 327 363 471 729 2187 2199 3063 4359 4375 5571
 </pre>