An integer n, such as 1128, is called "sorted" if its digits are in sorted order. Find the largest integer n such that both n and n² are sorted.

More generally it appears that any number of concatenated 3's (including zero) followed by any number of concatenated 6's (including zero) followed by a 7, when squared, will produce another "sorted" number.

Posted by Charlie on 2013-07-27 15:49:06