What is the value of 999999 * 999999 + 999991 * 999991 - 2 * 999999 * 999991? ( Is there a easier way? )
This is just (999999 - 999991)^2 = 8^2 → 64
.
Note that (a - b)^2 = a^2 + b^2 - 2*a*b
+501 
