63, because all others are perfect squares, or a whole number multiplied by itself is equal to that number 25 = 5 5 16 = 4 4 49 = 7 7 63 = (not a perfect square) 81 = 9 9
its 63 which is not like others ... you see 25 = 55 16 = 44 49 = 77 81 = 99 and .. 63 = 7*9 .... so from this we got that all the other numbers are perfect squares while 63 is not ..so it is not like the others ...
