Did you see >>5674 ? Your tests make it look like you didn't but I'm not sure.
What I was trying to point out is that you're incrementing n by 2 each time when I've found that every value of n from 1 upwards to some specific point (incrementing by 1) is valid for any given (x+n). I can't tell if you're taking every n into account considering you have n = n+/-2 in >>5631 this post. Maybe I'm reading it wrong. The f thing in my quick algebra is a mistake but that's not what I'm talking about.