Sunday, 29 November 2015

real analysis - Bijection from mathbbN to mathbbN s.t phi(n)nen2




Is it possible to find a bijection ϕ:NN such that nN,ϕ(n)n2




If it is not, how to prove, ϕL(N),NN,p>N,s.t.ϕ(p)=p2



(with L(N) the set of all bijections from N to N



Answer



Yes. Put ϕ(1)=2,ϕ(2)=1 and ϕ(n)=n for all n3.


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