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Gunnar_Zarncke comments on December 2014 Bragging Thread - Less Wrong Discussion

3 Post author: Morendil 30 November 2014 11:54PM

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Comment author: Gunnar_Zarncke 02 December 2014 12:41:56PM 2 points [-]

Let me tell you the 'story' behind the number I memorized:

286718338524635465625 (actually 21 digits which I got by something like 12345^5)

What is the pattern or story?

I grouped it as follows (the grouping is no fixed step, it happens as the 'story' unfolds):

286 718 3385 246 354 65 625

  • 286 is an old intel CPU

  • 7 is the lucky number of a friend (which incidentally has lots of old PCs possibly with 286s even)

  • 7+1 is 8 (which is my lucky number thus connecting us, his birthday is also very close to mine)

  • 33 is a double which stands out and 8 is the sum of the neighboring 3 and 5.

  • 246 35 are +2 stepped interleaved runs. The last 4 is between 3 and 5.

  • 65 was my hourly rate.

  • 625 is 5^4 a quite memorable number and just adds a 2 between the 65 before (thus backward connecting it).

In this case there is not much story but the patterns are memorable enough even without a real story,

Comment author: gjm 03 December 2014 05:28:53PM 1 point [-]

Note that the memorability of the last few digits is a direct consequence of the way you constructed the number (yes, it's 12345^5). The last 4 digits of n^5 when n ends in 5 are always among {0625,1875,3125,4375,6875,8125,9375}. If the digit before the 5 is even you always get one of {0625,3125,5625,8125}. At the very least, the final 3 digits are always a multiple of 125 and you probably recognize all of those.

Still, even a completely random number typically has lots of little patterns in it to help this kind of memorizing. For instance, I just generated a random 20-digit number: 66474746605022249923. The first things that occur to me, looking through it in order:

  • 66 4747 -- two pairs of repetitions
  • 466 -- overlapping 46 (one less than the 47 we just had) and 66 (same as first two digits, and a pair)
  • 050 -- symmetrical, all multiples of 5 (of which there aren't many among the digits :-))
  • 222 --- threefold repetition
  • 499 -- one less than 500
  • 23 -- not a particularly interesting number but e.g. the number of chromosome pairs you have.

(I also noticed in passing that 60502 is reminiscent of 6502, the processor in the first few computers I used. Lovely instruction set. Having some overlap between the features one notices is useful because it makes it easier to remember what order things come in.)

I tried the obvious experiment: after writing the above, could I look away from it and reproduce my 20-digit number? Why yes, I could; and still could a couple of minutes later. I think I'd find things like reversing the digits quite painful, though.

Comment author: Gunnar_Zarncke 03 December 2014 06:03:35PM 0 points [-]

Yes. Using x^y as a random number is bound to show patterns of this kind. I know enough number theory to recognize this. But it does alter the result only very slightly.

And yes. Your 'story' has the same basic structure as mine. I would have told it somewhat different but I think you got my approach. Note that it doesn't scale though. The major system beats it in that. But for small sequences of passwords it works nicely.

Comment author: LizzardWizzard 03 December 2014 08:59:16AM 0 points [-]

You made up this stories in a minute? Wow, fast system 1

Comment author: Gunnar_Zarncke 03 December 2014 12:49:43PM 1 point [-]

There is not that much to make up. For me numbers (digit sequences) are somewhat like words. And building a story from words is mostly easy - compare to this xkcd. Compare this:

  • 286 718 3385 246 354 65 625

  • cpu my-friend symmetric-hill stairs broken-stairs earning 5-squares.

The latter is not exactly how I read the digits but close enough to get an impression I hope. Constructing a story for the latter is easier than for the 'meaningless' digits themselves.

I guess it must be the same or rather much deeper for many mathematicians, esp. the number-theory ones. It was said about Ramanujan that every positive integer was one his personal friends.

Comment author: LizzardWizzard 06 December 2014 09:57:58AM 1 point [-]

Finally I mastered the skill) The trick was to put effort and make you sys2 to come up with a stories and then decode them into numbers again. I don't have deep mathematical and programming understanding like most of people here, so I had to use word almost time after time, for example "727" is almost Boeing 737