If number of turns of a solenoid is doubled while keeping all other factors constant, what would be the change in its self-inductance?

The self inductance of a solenoid is given as

L = μ₀N²A / l = L1

where

N is the number of turns of the solenoid

A is the area of each turn of coil

l is the length of the solenoid

and μ₀ is the permeability constant

so, if the number of turns were to be doubled the self inductance would be 

L2 =  μ₀  (2N)²A / l

or

L2 = 4L1

it would be quadrupoled or increase fourfold.