We study the behavior of all positive solutions of the difference equation in the title, where p is a positive real parameter and the initial conditions x - 2 ,x - 1 ,x 0 are positive real numbers. For all the values of the positive parameter p there exists a unique positive equilibrium x which satisfies the equation x 2 =x+p. We show that if 0<p<1 or p>=2 every positive bounded solution of the equation in the title converges to the positive equilibrium x. When 0<p<1 we show the existence of unbounded solutions. When p>=2 we show that the positive equilibrium is globally asymptotically stable. Finally we conjecture that when 1<p<2, the positive equilibrium is globally asymptotically stable.