Prime Numbers & The Sieve of Eratosthenes

Brett Berry

17910

many many many years ago, I took a math aptitude test and one of the problems had to do with square numbers…(50 years has blurred my memory as to the original problem, but the crux was that only a few numbers are possibly square…since any two numbers that end in zero, when multiplied together will end in 0, ONE 1x1 will end in 1 when multiplied together…2x2 ends in 4, 3x3 in 9, and 4 x4 in 6, 5x5 in 5, 6x6 in 6, 7x7 in 9, 8x8 in 4, 9x9 in 1…so if a number doesn’t end in 0,1,4,5, 6, or 9, it is not a perfect square. so 40% of all numbers are eliminated on inspection of the last digit.