And that, folks, is crackpottery in full action.
V = v/(sqrt(1 - v^2/c^2), V Newtonian, hence unlimited.
Let's try it.
Let  V =2c,  c = 1.
2 = v/sqrt(1 -v^2)  given.

4 = v^2 / (1-v^2)    (squaring)
v^2 = 4-4v^2          (multiply by 1-v^2 )
0 = 4 - 4v^2 - v^2   (subtract v^2)
   = 4-v^2(4-1)
   = 4 -3v^2
 3v^2 = 4
v^2 = 1.33
v = sqrt(1.33)
    = 1.155 >  1.