discrete function - onto and 1-1

Give a example of a function from N to N (naturals) that is
a) one-to-one and onto
b) onto but not one-to-one

What about ?
Which part does that answer?

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Originally Posted by pila0688

Give a example of a function from N to N (naturals) that is
a) one-to-one and ontoo

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An obvious answer: f(n)= n.

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b) onto but not one-to-one

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Try mapping each even number, 2n, into n and each odd number, 2n+ 1 into n.

That is, 1->1, 2->1, 3->2, 4->2, etc.

Would f(n) = n^2 be onto but not 1-1?