For every positive integer n, define the positive integer un by the condition that
un−1∑k=11k≤n<un∑k=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 vn≤un−1 so vn∑k=11k≤n, which is absurd, thus un = vn.
Answer
n<un∑k=11k⩽
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