Of course, and you only store odd numbers, and you can do all the smaller factors in a single pass. Nicely had already done some of these tweaks and I tried som

Of course, and you only store odd numbers, and you can do all the smaller factors in a single pass. Nicely had already done some of these tweaks and I tried some others, but it didn't change the overall problem: In the steady state you are still striding a huge array in memory and missing the cache with every access.