## Challenge: Can you memorize 67890 digits?

3.141592653589793238462643383279502884197169399375105820974944592307816406286208998628034825342117067982148086513282306647093844609550582231725359408128481117450284102701938521105559644622948954930381964428810975665933446128475648233786783165271201909145648566923460348610454326648213393607260249141273724587006606315588…You can tell from the first three or four digits that this whole bunch of numbers represents a simple idea, the ratio of a circle to its diameter, π. Now, if I say that the person who can memorize the most number of the decimals of pi can win a million dollar prize, what strategy do you think is the most effective, and how many decimals do you think are enough to win the prize?

One strategy that may come to your mind is creating little chunks of decimals of pi and memorize chunk by chunk. For example, the first 20 digits can be chunked into ‘31415,’ ‘92653,’ ‘58979,’ and‘32384.’ The last one or two digits of the previous chunk may cue you about the first one or two digits of the latter group. However, after you memorize a considerable number of decimals, you will find it difficult to continue because the digits cues start to repeat and you will experience too much retroactive interference, which describes the phenomenon that things memorized later may negatively affect your ability to recall something memorized earlier. A similar thing happens when you are trying to remember two people’s phone number. After you memorize the second phone number, the first one will appear to be a bit vague in your memory. You can choose to enlarge the group size from 5 digits to 10 digits to reduce the cue repetition, thus the retroactive interference can be reduced as you are using more digits as cues. However, you may still find it hard to continue after you reach a certain part when all the digits and cues entangle and you cannot recall them in a correct sequence, which is the key of memorizing pi. Due to the difficulties you find, you may come up with a reasonable estimation and wisely give up because it is kind of a waste of time. Read more…

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