June 28, 2016
Today’s exercise is in the style of Project Euler, so the rules are that your solution must not use more than a minute of computer time and that you can’t peek at the solution until you have the answer yourself.
Some numbers have the curious property that when they are squared, the number appears in the least-significant digits of the product. For instance, 6252 = 390625, and 71063762 = 50543227109376.
What is the sum of all numbers less than 1020 that have this curious property?