The number of onto functions from A = {a, b, c} to B = {1, 2, 3, 4} is __________.

Given: A function from A = {a, b, c} to B = {1, 2, 3, 4}

If a function from $A$ to $B$ is onto, then number of elements of $A \geq$ number of elements of $B$.

But here, number of elements of $A<$ number of elements of $B$

Thus, no onto function exist from A = {a, b, c} to B = {1, 2, 3, 4}.

Hence, the number of onto functions from A = {a, b, c} to B = {1, 2, 3, 4} is 0.