Question

Using digit sum rule, determine if 1626 is a perfect square.

Answer 1

Sum of digits in $1626$ is $1+6+2+6=15$
Upon adding again we get $1+5=6$.
The repeated digit sum of a perfect square is always 1, 4, 7 or 9.
Since the sum is 6 in 1626, it cannot be a perfect square