Recently, I looked up some grammar about the different counting systems for objects, animals, etc. the language has. I noticed that there were some exceptions for certain numbers.
As an example, if you count long cylindrical things, you use the number and ほん, so 2 pieces would be にほん.
But there are some exceptions with the numbers 1,3 6,8,10. I guess these numbers get rendaku`d, so 1 is いっぽん, 3 is さんぼん, etc.
I read the article about the rendaku, hoping that I would understand the reason behind it, but I got more confused afterward.
I also looked at the other counting words like さつ (for books), ひき (small animals) and noticed that in most of the cases the numbers 1,3,6,8,10 will get a rendaku.
Why is that so and if 3(さん )will get one, why wouldn`t 4(よん) get one? Is it just because of the pronunciation?