[BLACK-Dragon]

4. $p(n)= \dfrac{p(n-1)+1}{1-p(n)}$

$p(2)=-2$

$p(3)= -\dfrac{1}{3}$

$p(4)= \dfrac{1}{2}$

$p(5)= 3$

$\dfrac{p(2011)}{p(2554)}= \dfrac{1}{6}$