Well, this is something quite random, but I've found the equation to find the number of spaces between pillars on a wall. By pillars I can also mean lines like the picture as the "cover".

The equation is:

/ = Division (If you don't know)
P = # of Pillars Wanted
L = Length of Wall
S = Space between pillars

S = (L - P) / (P - 1)

If you don't believe this works, here:

S = (7 - 3) / (3 - 1)

That equals two. If you don't get it, look at the "cover" picture, there are two spaces between the lines like the equation says.

One last note, the length and pillars must either be both odd or both even, otherwise this equation will come out with a decimal, which is not possible in Minecraft (1.5 blocks sideways, for example).

I am not sure I am the only one who figured this out, but in hope that I am (no wannabe winners claiming this is theirs) the only one who knew about this until now, I call this the Whirl Equation, for myself, ShadowWhirl.

Have a good one!