Understanding the 'rem(n, 21) ~= 0' Expression

This expression means that the remainder when dividing n by 21 is not equal to 0.

The 'rem(n, 21)' part represents the modulo operation, which calculates the remainder of a division. In this case, it calculates the remainder when n is divided by 21. The '~= 0' part indicates that the remainder is not equal to zero.

Therefore, the expression 'rem(n, 21) ~= 0' implies that n is not divisible by 21. For example, if n = 25, then rem(25, 21) = 4, which is not equal to 0. This means 25 is not divisible by 21.