An integral domain is any commutative ring with no zero divisors (a,b are zero divisors if ab = 0 but a != 0, b != 0). In this case 2*2 = 0, so 2 is a zero divi

An integral domain is any commutative ring with no zero divisors (a,b are zero divisors if ab = 0 but a != 0, b != 0). In this case 2*2 = 0, so 2 is a zero divisor, so Z/4z = Z_4 is not an integral domain.