What number doesn't belong 21 41 81 11 19?

Answer 1

-- 11 doesn't belong, because it's the only one that's less than 19 .

-- 19 doesn't belong, because it's the only one without a ' 1 ' in the units place.

-- 81 doesn't belong because it's the only one that's greater than 80.

-- 21 doesn't belong because it's the only one with four distinct factors.

-- 41 doesn't belong because it's the only prime that's bigger than all the other primes in the group.