Open Thread for April 25, 2016; Happy Title 25

So we're looking at 25 this Monday
25 is 5 squared, and it has no other divisors. It is odd, like the square of every prime other than 2.

25 is the smallest square that is the sum of two smaller squares (9 & 16). Carpenters and others make fact of this property to draw large right angles, since this is a pythagorean triangle, with sides of 3, 4 and 5