Let abcd be one of the 9999 numbers 0001,0002,0003,…,9998,9999. Let abcd be an special number if ab−cd and ab+cd are perfect squares, ab−cd divides ab+cd and also ab+cd divides abcd. For example 2016 is special. Find all the abcd special numbers.
Note: If abcd=0206, then ab=02 and cd=06. number theoryPerfect Squarescono sur