The given function f:N×N⟶N is defined by f(m,n)=2m−1(2n−1),∀(m,n)∈N×N Now, let f((a,b))=f((c,d)), where a,b,c,d∈N ⇒2a−1(2b−1)=2c−1(2d−1) ⇒2a⋅b−2a−1=2c⋅d−2c−1⇒(a,b)=(c,d) ∴f is a one-one function. Now as 2m−1 is a even number for ∀m∈N−{l} and (2n−1) is a odd number for ∀N∈N, so the every natural number can be obtain by the for 2m−1.(2n−1) for some combination of (m,n), so f is an onto function.