Actually... I'm not sure if you use the base stat or the actual stat... Smogon says actual, but I'll give you both. The equation for the actual stat is...
2x + 5
If x is the base stat. So, if we double that...
2(2x + 5) = 4x + 10, 4*50 + 10 = 210
OK. But if we use Smogon's way... Azumarill's max attack is 218...
218 * 2 = 436
About the same... but higher.
