[seqfan] Re: Common terms in An and Am

[Olivier Gerard]

Dear Zak,

Here is an equivalent of Robert's maple example in Mathematica
This is not production quality code, just oneliners to get the job done.
Use with caution and discretion.

(* utility code to evaluate before other instructions *)
OEISAnumbase[n_Integer]:=IntegerString[n,10,6]

ReadOEISBfile[n_Integer]:= ReadList["https://oeis.org/
"<>"A"<>OEISAnumbase[n]<>"/b"<>OEISAnumbase[n]<>".txt",{Number,Number}]

findInBfile[oeisb_List,k_Integer]:= Cases[oeisb,{_,k}]


(* Reading a few bfiles *)
b000110= ReadOEISBfile[110];
b000225= ReadOEISBfile[225];

(* display first values *)

Last/@Take[b000110,10]
{1,1,2,5,15,52,203,877,4140,21147}

Last/@Take[b000225,10]
{0,1,3,7,15,31,63,127,255,511}


(* find identical values at identical indices)

Intersection[b000110,b000225]
{{1,1},{4,15}}


(* read other bfiles *)
b002821=ReadOEISBfile[2821];
b002843=ReadOEISBfile[2843];

(* extract list of values *)
v002821 = Last/@b002821;
v002843 = Last/@b002843;

(* find identical values between the two lists *)
Intersection[v002821,v002843]
{1,253}


(* display the indices of a value in a loaded bfile *)
findInBfile[b002821, 253]
{{40,253}}


findInBfile[b002843, 253]
{{10,253}}



Regards,

Olivier


On Thu, Dec 7, 2023 at 4:21 PM zak seidov via SeqFan <seqfan at list.seqfan.eu>
wrote:

>  Maple is great but I use Mathematica or Pari on elementary level, sorry
>     On Thursday, December 7, 2023 at 04:24:55 AM GMT+2, israel at math.ubc.ca
> <israel at math.ubc.ca> wrote:
>
>  Here is Maple code to find the terms common to two sequences.
>
> OEISCommonTerms(num1, num2) finds the list of all pairs [i,t] such that
> Anum1[i] = Anum2[i] = t, where num1 and num2 are integers of up to 6
> digits. The b-files will be used if present, otherwise just the Data. An
> error will occur if these sequences are not in OEIS. Thus
>
> > OEISCommOnTerms(110, 225);
>
>     [[1,1],[4,15]]
>
> because A000110(1) = A000225(1) = 1 and A000110(4) = A000225(4) = 15 are
> the terms that occur at the same index in both A000110 and A000225.
>
>
> OEISIntersect(num1, num2) finds the set of all integers that occur
> at least once in both Anum1 and Anum2.  Thus
>
> > OEISIntersect(2821, 2843);
>
>       {1, 253}
>
> because A002821(1) = A002843(0) = A002843(1) = 1 and A002821(40) =
> A002843(10) = 253.
>
> getbfile:= proc(anumber)
>  local bfile,nstr,S,L,B,t,found;
>  nstr:= sprintf("%6d",10^7+anumber)[-6..-1];
>  bfile := StringTools:-Substitute(sprintf("https://oeis.org/A%s/b%s.txt",
>         nstr$2)," ","0");
>  S:= URL:-Get(bfile);
>  fclose(bfile);
>  if StringTools:-Search("Sorry, the page you requested was not found.",S)
> <> 0 then error "No sequence %1", nstr fi;
>  S:= StringTools:-Split(S,"\n");
>  found:= false;
>  for t in S do
>   L := sscanf(t,"%d %d");
>   if nops(L) = 2 then
>   B[L[1]]:= L[2]; found:= true;
>   fi
>  od;
>  if not found then error "No data" fi;
>  eval(B)
> end proc:
> OEISCommonTerms:= proc(num1,num2)
>   local R, A1, A2, I1, I2, i;
>   A1:= getbfile(num1);
>   A2:= getbfile(num2);
>   I1:= [indices(A1)];
>   I2:= [indices(A2)];
>   R:= NULL;
>   for i from max(min(I1),min(I2)) to min(max(I1),max(I2)) do
>     if A1[i] = A2[i] then R:= R, [i,A1[i]] fi
>   od;
>   [R]
> end proc:
> OEISIntersect:= proc(anum1, anum2)
>   local S1, S2;
>   S1:= convert(getbfile(anum1),set);
>   S2:= convert(getbfile(anum2),set);
>   S1 intersect S2;
> end proc:
>
> Cheers,
> Robert
>
>
>
> On Dec 6 2023, Neil Sloane wrote:
>
> >why not download the two b-files and use Maple or whatever to find their
> >intersection
> >
> >a few lines of Unix shell commands will do it automatically
> >
> >Best regards
> >Neil
> >
> >Neil J. A. Sloane, Chairman, OEIS Foundation.
> >Also Visiting Scientist, Math. Dept., Rutgers University,
> >Email: njasloane at gmail.com
> >
> >
> >
> > On Wed, Dec 6, 2023 at 9:32AM zak seidov via SeqFan
> > <seqfan at list.seqfan.eu> wrote:
> >
> >> Dear all,Is it any possibility to find common terms in any two OEIS
> >> sequences, e.g., from their bfiles?Thanks a lot,Zak
> >>
> >> --
> >> Seqfan Mailing list - http://list.seqfan.eu/
> >>
> >
> >--
> >Seqfan Mailing list - http://list.seqfan.eu/
> >
> >
>
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