The first iteration vectorized with numpy is the best solution imho. The only additional optimization is using modulo 9 to give you a sum of digits mod 9; that should filter out approximately 1/9th of numbers. The digit summing is the slow part so reducing the number of values there results in a large speedup. Numpy can do that filter pretty fast as `arr = arr[arr%9==3]`

With that optimization its about 3 times faster, and all of the none numpy solutions are slower than the numpy one. In python it almost never makes sense to try to manually iterate for speed.