P Value from Pearson r

However, there is slightly deviation for smaller Cl values... Looks like they become numb to the left..

it would be nice to see how result behave for Cl --> 0 so I could modificate formula.
But there is no enough data.

From the picture you can see Table values approaching to 1 (or some other value) while Formula values going to infinity.

Of course, if you don't need lower values then you can use this but if you need higher precision (espetially in the middle of the table) then data should be separated for N over or below 10.