This is a telescoping series. Let Sn be the n-th partial sum of the series. Sn=k=1∑n(k1−k+11) Sn=(11−21)+(21−31)+(31−41)+⋯+(n1−n+11) The intermediate terms cancel out, so we are left with:
Sn=1−n+11 The infinite sum is the limit of the partial sums as n approaches infinity: k=1∑∞(k1−k+11)=n→∞limSn=n→∞lim(1−n+11) Since limn→∞n+11=0, we have: n→∞lim(1−n+11)=1−0=1