Take the number 287. Find the floor of its square root: sqrt(287)=16.941074... it's 16. Now get the factors of 287 = 7*41. Subtract the first prime factor from the floor of the square root: 7-16 = -9. Now subtract the second prime factor from the floor of the square root: 41-16 = 25. Add those values together: -9+25 = 16. It's the same as the floor of the square root. But it doesn't always work out that way.