積分判別法-The Integral Test


https://math.stackexchange.com/questions/2858067/upper-bound-of-p-series

https://courses.lumenlearning.com/calculus2/chapter/the-p-series-and-estimating-series-value/

兩個重要級數（p級數和幾何級數）
https://zhuanlan.zhihu.com/p/512491433
微積分II 積分判別法(The Integral Test)
https://zhuanlan.zhihu.com/p/183969735