What were the mathematical techniques used for estimating euler number e upto 18 trillion trillion digits ?? While surfing, I came across this mathematical term: **$$(1+9^{-4^{6*7}})^{3^{2^{85}}}$$** which approximately equals to the mathematical constant **_e_** ( **Euler's number** ) upto **_18 trillion trillion digits_**. What were the mathematical techniques used to approximate **_e_** upto 18 trillion trillion digits ?? What were the mathematical techniques used in finding the term **$(1+9^{-4^{6*7}})^{3^{2^{85}}}$**??

**Hint:**

$$\lim_{x \to \infty} (1+1/x)^x = e$$

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**Hint 2:**

> $$\frac{1}{9^{-4^{6*7}}} = 3^{2^{85}}$$

Also, watch this video by Numberphile on the topic