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Problems for Chapter VII
                                                                   N
                                                            Problems for Chapter VII   75

                        1. Given that    a n  converges, prove that    a n   o(N).
                                          n                        n 1
                                                                            −1
                        2. Given that    a n  converges and that a n − a n−1 >  , prove that
                                          n                                 n
                           a n → 0.
                                                                              ε
                        3. Show that d(n), the number of divisors of n,is O(n ) for every
                           positive ε.
                                                         1
                        4. In fact, show that d(n)   n  log log n  .
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