Question 16
A *triangular number* is a positive integer that can be expressed in the form $t_n=1+2+3+\cdots+n,$ for some positive integer $n.$ The three smallest triangular numbers that are also perfect squares are $t_1=1=1^2,$ $t_8=36=6^2,$ and $t_{49}=1225=35^2.$ What is the sum of the digits of the fourth smallest triangular number that is also a perfect square?