1. The problem statement, all variables and given/known data How can one find an equivalent of 1/n^(a) in the neighborhood of +infinity? And what's the method in general to get an asymptotical development of a sequence? 2. Relevant equations The result is: 1/n equivalent to ln(n+1)-ln(n) 1/n^a equivalent to (1/a-1)*(1/n^(a-1)-1/(n+1)^(a-1) if a is different from 1. 3. The attempt at a solution I tried to use Taylor Young with f:=x->x in the neighborhood of 0 (this is useless) Thanks a lot for your help.