How to remember e to 20 decimal places

September 18, 2021 by Joshua
in Nature

One of my graduate school professors told us the following way to remember the natural logarithm/exponential number e to 20 decimal places, which I’ll share with you what some scientists consider fun.

I forget which professor told us, but I think I was at Penn, which means 1993-94. He only told us once. It stuck effortlessly, so I consider it effective. And fun.

How to remember e to 20 decimal places

Everyone remembers 2.7.

Years you can chunk as a single number, so with the year 1828, you get the next eight digits because it repeats: 18281828. So remembering one number gives you:


Next remember 45, which gets you the next eight digits because you double it, then repeat it, then halve it: 45904523. Now you’re at:


Then, you just have to remember 536. A professor taught it to me in graduate school (physics) and I think he justified remembering those three kept the number of numbers to remember at the number of objects they say the average person can keep in their acting memory at once:


He didn’t go to the next number, but I looked it up, found it was 0, and concluded I could claim a free number, which meant I also checked that the following number was below 5 so that 0 wouldn’t round up, so:

2.718281828459045235360 (then something less than 5)

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