f(1) = 1

f(2) = 1

f(3) = 2

f(4) = 2

f(5) = 3

f(6) = 3

Since at different values of x we get same value of y ∴f(n) is many –one

And range of f(n) = N = N(codomain)

∴ the function f: N → Z, defined by

is both many - one and onto.