Program to find Primes of the form prime(n+2) * prime(n+1) - prime(n) +- 1.

[Chris Angelico]

On Fri, Oct 5, 2018 at 12:47 AM Alister via Python-list
<python-list at python.org> wrote:
>
> On Thu, 04 Oct 2018 09:44:01 +0100, Tony van der Hoff wrote:
>
> > On 04/10/18 09:31, Alister via Python-list wrote:
> >> On Wed, 03 Oct 2018 09:43:07 -0700, Musatov wrote:
> >>
> >>> On Wednesday, October 3, 2018 at 11:12:43 AM UTC-5, Michael Torrie
> >>> wrote:
> >>>> On 10/03/2018 09:26 AM, Musatov wrote:
> >>>>> I don't even know where to begin! (I'm reading the Dummies book)
> >>>>
> >>>> If you have no experience in computer programming, it's going to be a
> >>>> steep learning curve.
> >>>>
> >>>> But your first step is to learn Python and how to write programs in
> >>>> it.
> >>>> That book and others will help with that.  You'll have to write lots
> >>>> of simple programs unrelated to primes along the way that help you
> >>>> understand programming concepts.
> >>>>
> >>>> If you already have experience in other languages, the task will be
> >>>> easier.
> >>>>
> >>>> Computer programming is quite natural to some (small children seem to
> >>>> get it much easier than us adults), but I've seen others struggle to
> >>>> grasp the abstract concepts for years.
> >>>>
> >>>> Once you've grasped basic Python programming, you can return top the
> >>>> original problem at hand.  Start by identifying the process or
> >>>> algorithm that would find these primes. In other words, how would you
> >>>> do it on pen and paper?  Computer programs are not magic.  They are
> >>>> only expressions of human thinking. Often some very smart
> >>>> mathematicians have come up with powerful algorithms (a step-by-step
> >>>> process) to do these things,
> >>>> and your job as a programmer is to turn this mathematical process
> >>>> into a computer program using things like loops and Boolean logic.
> >>>> How would you find these primes using your pen, paper, and
> >>>> calculator?
> >>>
> >>> Literally, how I found them was taking a list of primes and checking
> >>> if the calculations with the lesser primes resulted in numbers also
> >>> further along on the list.
> >>>
> >>> Another way I guess would be to do the calculations then check if the
> >>> number is prime.
> >>
> >> That is exactly how you do it with in a program.
> >>
> >> create a loop & check to see if the target number can be divided by
> >> each possible divisor in turn .
> >> for large numbers this will take a large number of tests (hey that is
> >> why you have the computer do them, it is faster than you & does not get
> >> bored ;-) ) there are numerous tricks for speeding up this process once
> >> you have the basic working.
> >>
> >> start by testing small numbers & then use your real data once you have
> >> something that works
> >>
> >> as a starter a simple loop in python could be as follows
> >>
> >> for x in xrange(10):
> >>      print x
> >>
> >> once you have an outline of a program post it back here if things dont
> >> work as expected
> >>
> >>
> > Two lines, two errors! To save the noob a lot of head-scratching, that
> > should be:
> > for x in range(10):
> >
> > If you're running python 3, as you should do for any new project:
> >       print( x )
>
> perfectly legit python 2.7
> I probably should have considered writing python 3 compatible code but
> range operates differently on the 2 versions & would be a poor choice for
> python 2 when numbers get larger

For a loop with a print in it, I'd definitely just use range(). It'll
work on all versions, and long before you run into problems with the
RAM usage on Py2, you've spammed your terminal so much that you're
waiting for it :)

ChrisA