Let $S=\{1,2,3\}$. Consider the following open sentences over the domain $S$ :
$P(n): \frac{(n+4)(n+5)}{2}$ is odd.
$$
Q(n): 2^{n-2}+3^{n-2}+6^{n-2}>(2.5)^{n-1} .
$$
Determine three distinct elements $a, b, c$ in $S$ such that $P(a) \Rightarrow Q(a)$ is false, $Q(b) \Rightarrow P(b)$ is false and $P(c) \Leftrightarrow Q(c)$ is true.