Square Numbers Sudoku (Fun With Sudoku #35)

This Square Numbers Sudoku, I created for 21st Indian Sudoku Mock Test. This is very old Sudoku which was on my notebook without getting published. After some many years I am publishing this Sudoku on this blog.
Sudoku Grand Prix Championship 2015 is going to start early next year with the instruction booklet of first round is already published. It contains many interesting Sudoku variations with two Sudoku variations Round Off Sudoku and Mathrax Sudoku being the new variations. I will be creating some of these unknown variations which are appearing in this championship soon and will publish these puzzles under The League of Extraordinary Ladies and Gentlemen. Do keep watch on this blog for these new variations.
This Square Numbers Sudoku I am posting as 35th Sudoku in Fun With Sudoku Series.

Rules of Square Numbers Sudoku

Classic Sudoku Rules apply. Additionally greyed squares can only contain square numbers i.e. the number which we can get after doing square of a number. In other words greyed cells can contain only 1, 4,9 numbers.