[Jprogramming] Unforgettable times

[Roger Hui]

226: the first emirprime which is the successor of
a perfect square and the precedessor of a prime.

http://mathworld.wolfram.com/Emirpimes.html



----- Original Message -----
From: Randy MacDonald <ramacd at nbnet.nb.ca>
Date: Saturday, August 22, 2009 13:42
Subject: Re: [Jprogramming] Unforgettable times
To: Programming forum <programming at jsoftware.com>

> What is memorable about 226?
> 
> 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 <km at math.uh.edu>
> > Date: Saturday, August 22, 2009 5:27
> > Subject: Re: [Jprogramming] Unforgettable times
> > To: Programming forum <programming at jsoftware.com>
> >
> >   
> >> 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