Magnetic field for a single-layer solenoid

[asdf1]

does anybody know why the magnetic field for a single-layer solenoid of a point in the middle of the solenoid axial field is
H=[(4pini)/(10L)]*{[L+2x/[2(D^2+(L+2x)^2]^(0.5) +
[L-2x/[2(D^2+(L-2x)^2]^(0.5)}
where L is the length of a finite solenoid, D is the diameter

 

[Physics Monkey]

You can calculate the on axis magnetic field of a current loop. To obtain the on axis field of a finite solenoid, just integrate.

 

[asdf1]

i did... I'm stuck on where does[(4pini)/(10L)] come from?