Monday, 19 October 2015

sequences and series - Convergence of un defined by $sumlimits_{k=1}^{u_n-1}frac{1}kleq n





For every positive integer n, define the positive integer un by the condition that
un1k=11kn<unk=11k
Let wn=1un. Does the sequence (wn) converge and how to prove rigorously it does?




What I did:



I proved that un exists and is unique, and that u1=2 and u2=4.




Proof of uniqueness:



Suppose that un>vn satisfying the defining condition, then vnun1 so vnk=11kn, which is absurd, thus un = vn.


Answer



n<unk=11k


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