I wonder whether 1729 was a number Ramanujan had met before, or merely a number
whose properties he flashed on as soon as he saw it! For a while 1 7 2 9 will
be on your personal list of "times I know".
Roger Hui wrote:
> The problem is that _every_ number has something
> notable about it, so that each number is "unforgettable"
> and consequently it's hard to remember any single
> one of them.
>
> 0000 all zeros
> 0001 first counting number
> 0002 first prime number
> 0003 first odd prime
> 0004 first composite number
> ...
> 24 60 #: ?. */ 24 60
> 1 6
>
> 0106 first number greater than 100 with 2 prime factors
>
> etc.
>
> You have most likely heard of the story about Hardy
> and Ramanujan. One day Hardy took a taxi to visit
> Ramanujan. On arriving Hardy told Ramanujan that
> the taxi had the 4-digit number n on its license plate,
> a thoroughly unremarkable number. Ramanujan
> immediately remarked that n is the first number that ... .
> I forget what n or the property was, something like,
> n is the first number that can be written as the sum
> of two perfect cubes in two different ways, something
> typically Ramanujanish.
>
> Yes, that was it:
>
> c=: i*i*i=: >:i.200
> t=: (</~i.200) * +/~c
> d=: </.~ ,t
> (2=#&>d)#d
> +---------+---------------+---------------+---------+--
> |1729 1729|1092728 1092728|3375001 3375001|4104 4104| ...
> +---------+---------------+---------------+---------+--
> <./ {.&> (2=#&>d)#d
> 1729
> I. , 1729 = t
> 11 1609
> 1 + (#t) #: 11 1609
> 1 12
> 9 10
> +/ 1 12 ^ 3
> 1729
> +/ 9 10 ^ 3
> 1729
>
> Now that I have worked out the number I can find the
> story on the net: http://en.wikipedia.org/wiki/1729_(number)
>
> p.s. In my youth, when I needed to remember a (5-digit)
> number for a time, I would try to compute its largest
> prime factor by mental calculation. Try it and you'll
> see why that works.
>
>
>
> ----- Original Message -----
> From: Kip Murray <[email protected]>
> Date: Saturday, August 22, 2009 5:27
> Subject: Re: [Jprogramming] Unforgettable times
> To: Programming forum <[email protected]>
>
>> To narrow the puzzle,
>>
>> times 3 4 5 NB. Unforgettable
>> 1 6 2 0
>> 1 8 1 2
>> 1 2 0 7
>> timedata i. 1 8 1 2
>> 4
>> times i.8
>> 1 2 3 4
>> 1 4 1 4
>> 1 4 2 8
>> 1 6 2 0
>> 1 8 1 2
>> 1 2 0 7
>> 1 2 3 4
>> 1 4 1 4
>>
>> You are encouraged to choose your own unforgettable times seen
>> on a 24-hour
>> digital clock.
>>
>>
>> Kip Murray wrote:
>>> Who could forget
>>>
>>> times 3 4 5
>>> 1 6 2 0
>>> 1 8 1 2
>>> 1 2 0 7
>>>
>>> ?
>>>
>>> Kip Murray wrote:
>>>> Write a verb that produces unforgettable times on a 24-hour
>> digital clock: who
>>>> could forget an appointment at 12:34 or 14:14 or 14:28
>> ? It's too bad that
>>>> 31:41 , 27:18 and 69:31 do not fit on the clock.
>>>>
>>>> times 0
>>>> 1 2 3 4
>>>> times 0 1
>>>> 1 2 3 4
>>>> 1 4 1 4
>>>> times i. 5
>>>> 1 2 3 4
>>>> 1 4 1 4
>>>> 1 4 2 8
>>>> 1 2 3 4
>>>> 1 4 1 4
>>>> NB. Oh, well, you will do
>> better than this
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