Which is the largest?

The general expression for the four terms is $a_n = \dfrac {(n+1)^2}n$ , where $n = 1, 2, 3, 4$ . Consider the quotient $\dfrac {a_{n+1}}{a_n}$ , we have:

$\begin{aligned} \frac {a_{n+1}}{a_n} & = \frac {(n+2)^2}{n+1} \times \frac n{(n+1)^2} \\ & = \frac {n^3+4n^2+4n}{n^3+3n^2+3n+1} > 1 & \small \color{#3D99F6}{\text{for }n \ge 1} \end{aligned}$

Therefore, $a_n$ increases with $n$ , so the largest of the four terms is $a_4 = \boxed{\dfrac {5^2}4}$ .