Actually Welcome to the Concept of the Inverse of real function.
Let's consider here, g(n) = y ,
so we get as,
no, cubing the power both side we get as,
=>
now,
so finally, we get as,
=>
hence,here, n = inverse of the g(n) function.
so,
g^-1 (n) = 2y^3+1.
