997 * 1003 = (1000 - 3)(1000 + 3) = 1000^2 - 3^2
1999 * 2001 = (2000 - 1)(2000 + 1) = 2000^2 - 1^2
40003 * 39997 = (40000 + 3)(40000 - 3) = 40000^2 - 3^2
997 * 1003 = (1000 - 3)(1000 + 3) = 1000^2 - 3^2
1999 * 2001 = (2000 - 1)(2000 + 1) = 2000^2 - 1^2
40003 * 39997 = (40000 + 3)(40000 - 3) = 40000^2 - 3^2