Originally Posted by

**ThePerfectHacker** Numbers of the form 4k,4k+1,4k+3 can always be expressed as a difference of squares.

Remove the odd numbers for they can always be expressed as difference of squares are you have,

314159266

314159268

Divide them by 4 and find the one which leaves a remainder of 2.

Since both are even they leave either no remiander or 2.

Thus, find the number not divisible by 4.

The trick is to look at the last two digits,

66----> Not Divisible

68----> Yes Divisible

Thus, the answer is,

314159266