Product of Two Triangular Numbers to make Square/Mistake

Source Work

 * The Dictionary
 * $15$
 * $15$

Mistake

 * For every triangular number, $T_n$, there are an infinite number of other triangular numbers, $T_m$, such that $T_n T_m$ is a square. For example, $T_3 \times T_{24} = 30^2$.

This is incorrect.

It is supposed that this is a misprint for:
 * $T_2 \times T_{24} = 30^2$

which is correct.