Added special cases for Python3, Python, PyPy and LuaJIT.

Makefile

@@ -18,8 +18,11 @@ clean:
 
 test: all
 	@ time -f "%C : %E seconds" ./a.out $(ROUNDS) > /dev/null
-	@ [ -n "$$(which python3)" ] && time -f "%C : %E seconds" ./prime.py $(ROUNDS) > /dev/null
+	@ [ -n "$$(which python)" ] && time -f "%C : %E seconds" ./prime.py $(ROUNDS) > /dev/null
+	@ [ -n "$$(which python3)" ] && time -f "%C : %E seconds" python3 prime.py $(ROUNDS) > /dev/null
+	@ [ -n "$$(which pypy)" ] && time -f "%C : %E seconds" pypy  prime.py $(ROUNDS) > /dev/null
 	@ [ -n "$$(which lua)" ] && time -f "%C : %E seconds" ./prime.lua $(ROUNDS) > /dev/null
+	@ [ -n "$$(which luajit)" ] && time -f "%C : %E seconds" luajit prime.lua $(ROUNDS) > /dev/null
 	@ [ -n "$$(which php)" ] && time -f "%C : %E seconds" ./prime.php $(ROUNDS) > /dev/null
 	@ [ -n "$$(which php7.0)" ] && time -f "%C : %E seconds" php7.0 prime.php $(ROUNDS) > /dev/null
 	@ [ -n "$$(which ruby)" ] && time -f "%C : %E seconds" ./prime.rb $(ROUNDS) > /dev/null

prime.py

-#!/usr/bin/env python3
+#!/usr/bin/env python
+from __future__ import (absolute_import, division,
+                        print_function, unicode_literals)
+
+
 def is_prime(x):
     from math import sqrt, ceil
     if sqrt(x).is_integer():
         return False
-    for i in range(2, ceil(sqrt(x))):
+    for i in range(2, int(ceil(sqrt(x)))):
         if x % i == 0:
             return False
     return True