Ralph Likes 25 But Not 24; He Likes 400 But Not 300; He Likes 144 But Not 145. Which Does He Like?10 50 124 200 1600

Ralph likes square numbers. He likes 25 (5²), 400 (20²) and 144(12²).
Of the listed numbers only 1600 is a square (40²) - so this is the one Ralph likes.