If anyone wants to beef up the rosetta entry
https://www.rosettacode.org/wiki/Circular_primes#J this might be a
good opportunity.
(That said, note that the site was down for most of yesterday. I have
not yet heard what happened, but possibly it was overloaded with
visitors.)
--
Raul
On Sun, Sep 24, 2023 at 3:30 AM Jan-Pieter Jacobs
<janpieter.jac...@gmail.com> wrote:
>
> Ha, I fixed my wrong solution of yesterday:
>
> cond=: # = [: (!@# % [: */ !@#/.~) 10 #.inv {.
> primegroups=.(#~cond&>) (</.~ <@(/:~)@(10&#.inv)"0) i.&.(p:^:_1) 1e6
> _3]\primegroups
> +-----------+-----------+-----------+
> |2 |3 |5 |
> +-----------+-----------+-----------+
> |7 |11 |13 31 |
> +-----------+-----------+-----------+
> |17 71 |37 73 |79 97 |
> +-----------+-----------+-----------+
> |113 131 311|199 919 991|337 373 733|
> +-----------+-----------+-----------+
> (note: "primegroups=. ... 1e6" is a single line). Actually 2 3 5 7 and
> 11 also are (trivially so) all permutations of their digits.
>
> Fun challenge, more involved than it seemed to at first sight. Also fun to
> see that these are the only groups, at least until 1e8.
>
> Jan-Pieter
>
> On Sat, 23 Sept 2023, 19:33 'Pascal Jasmin' via Programming, <
> programm...@jsoftware.com> wrote:
>
> > pf 19 has at least 1 solution
> >
> > # 1 ,^:(0 = 1&p:@:(10&#.)@])(^:100) 1 1 1
> >
> > 19
> >
> > 1 p: 1111111111111111111x
> > 1
> > On Saturday, September 23, 2023 at 01:18:44 p.m. EDT, 'Pascal Jasmin'
> > via Programming <programm...@jsoftware.com> wrote:
> >
> > there is a bug in your p 3... 793 is not prime.
> > An approach that can be improved upon in speed:
> >
> > perm =: i.@! A. i.
> >
> > raveltillCS =: 1 : ',/^:(m < #@$)^:_' NB. repeat ravel until count of
> > shape = m
> >
> > p2 =: 1 3 7 9 ~.@:(,/^:(2 < #@$)^:_@:(/:~"1@:({ )~&:>)) (<0 1 2 3) { @:#~
> > ] NB. unique combinations(?) of digits (y is # of digits) that can form
> > primes
> > pf =: (perm (] #~ *./@:(1&p:)@:(10&#.)@:~.@:{"_ 1) p2) NB. filtered for
> > all permutations of combinations being prime.
> >
> >
> > pf 3
> >
> > 1 1 3
> >
> > 1 9 9
> > 3 3 7
> > pf 4 5 6 7 8 9 has no results
> > pf 10 takes a long time. also no results.
> >
> >
> >
> > On Saturday, September 23, 2023 at 01:54:28 a.m. EDT, 'Skip Cave' via
> > Programming <programm...@jsoftware.com> wrote:
> >
> > Here's a verb p(n) to produce all n-digit primes with the same digits:
> >
> > odo=:#: i.@(*/)
> >
> > p=:{{(#~1&p:)10#.(odo y#4){1 3 7 9}}
> >
> >
> > try it:
> >
> > p 2
> >
> > 11 13 17 19 31 37 71 73 79 97
> >
> > p 3
> >
> > 113 131 137 139 173 179 191 193 197 199 311 313 317 331 337 373 379 397 719
> > 733 739 773 797 911 919 937 971 977 991 997
> >
> > p 4
> >
> > 1117 1171 1193 1319 1373 1399 1733 1777 1913 1931 1933 1973 1979 1993 1997
> > 1999 3119 3137 3191 3313 3319 3331 3371 3373 3391 3719 3733 3739 3779 3793
> > 3797 3911 3917 3919 3931 7177 7193 7331 7333 7393 7717 7793 7919 7933 7937
> > 7993 9133 9137 9173 9199 9311 9319 9337 9371 9377 9391 9397 9719 9733 9739
> > 9791 9931 9973
> >
> > p 5
> >
> > 11113 11117 11119 11131 11171 11173 11177 11197 11311 11317 11393 11399
> > 11717 11719 11731 11777 11779 11933 11939 11971 13171 13177 13313 13331
> > 13337 13339 13397 13399 13711 13799 13913 13931 13933 13997 13999 17117
> > 17137 17191 17317 17333 17377 17393 17713 17737 17791 17911 17939 17971
> > 17977 19139 19319 19333 19373 19379 19391 19717 19739 19777 19793 19913
> > 19919 19937 19973 19979 19991 19993 19997 31139 31177 31193 31319 31333
> > 31337 31379 31391 31393 31397 31771 31793 31799 31973 31991 33113 33119
> > 33179 33191 33199 33311 33317 33331 33377 33391 33713 33739 33773 33791
> > 33797 33911 33931 33937 33997 37117 37139 37171 37199 37313 37337 37339
> > 37379 37397 37717 37799 37991 37993 37997 39113 39119 39133 39139 39191
> > 39199 39313 39317 39371 39373 39397 39719 39733 39779 39791 39799 39937
> > 39971 39979 71119 71171 71191 71317 71333 71339 71399 71711 71713 71719
> > 71777 71917 71933 71971 71993 71999 73133 73331 73379 73771 73939 73973
> > 73999 77137 77171 77191 77317 77339 77377 77711 77713 77719 77731 77773
> > 77797 77933 77977 77999 79111 79133 79139 79193 79319 79333 79337 79379
> > 79393 79397 79399 79777 79939 79973 79979 79997 79999 91139 91193 91199
> > 91331 91373 91393 91397 91711 91733 91771 91939 91997 93113 93131 93133
> > 93139 93179 93199 93319 93337 93371 93377 93719 93739 93911 93913 93937
> > 93971 93979 93997 97117 97171 97177 97373 97379 97397 97711 97771 97777
> > 97919 97931 97973 99119 99131 99133 99137 99139 99173 99191 99317 99371
> > 99377 99391 99397 99713 99719 99733 99793 99971 99991
> >
> > Skip Cave
> > Cave Consulting LLC
> >
> >
> > On Sat, Sep 23, 2023 at 12:26 AM Richard Donovan <rsdono...@hotmail.com>
> > wrote:
> >
> > > Hi
> > >
> > > I am trying to develop a program to find primes with n digits abc such
> > > that acb bac bca cab and cba are also primes. (obviously trivial if aaa
> > is
> > > prime!).
> > >
> > > An example with n=3 is
> > >
> > > 1 p: 199 919 991
> > >
> > > 1 1 1
> > >
> > > These primes are thin on the ground since they cannot contain any of the
> > > digits 2 4 5 6 8 or 0 and I am wondering if it would be best to construct
> > > numbers omitting those containing those prohibited digits, or test every
> > > comination of p: i. n which seems wasteful, especially since I want to
> > find
> > > all such primes below one million.
> > >
> > > Can anyone see an efficent way to produce this?
> > >
> > > Thanks in advance,
> > >
> > > Richard
> > > ----------------------------------------------------------------------
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> > >
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