Inverse factorial summation

Question

Find the sum $$\sum_{n=0}^\infty \dfrac1{n!}$$

Sorry, I couldn't find the symbol for Sigma.

Sigma(1/n!) I tried this but couldn't do it.

Any suggestions for the problem are welcome.

Answer 1

$$e^x=\sum_{n=0}^{+\infty}\dfrac{x^n}{n!}$$ So for $x=1$ you have: $$e=\sum_{n=0}^{+\infty}\dfrac{1}{n!}$$

Answer 2

The answere is the number e. Just use the Taylor-Lagrange theorem on the exponential fonction.