MathCastle
CalculusHardInfinite Sequences and Series

Infinite Sequences and Series · Hard problem

A machine's cumulative wear follows the partial sums SN=∑n=1N1n!S_N=\displaystyle\sum_{n=1}^N\dfrac1{n!} of a series whose total, as N→∞N\to\infty, is exactly e−1e-1 (using ∑n=1∞1n!=e−1\displaystyle\sum_{n=1}^\infty\dfrac1{n!}=e-1). After how many terms NN does the partial sum SNS_N first reach at least 99%99\% of that total?