login
The OEIS is supported by the many generous donors to the OEIS Foundation.

 

Logo
Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A082123 Smallest difference > 1 between d and p/d for any divisor d of the partial product p of the sequence, starting with 17. 2

%I #14 May 21 2015 10:38:26

%S 17,16,26,36,76,94,432,37220,996768,158267352,973348166592,

%T 8429202561226344,419324164827901536306744,

%U 339991740461303603766175692597227316,12025891484499365294341150949542442100059557280661504

%N Smallest difference > 1 between d and p/d for any divisor d of the partial product p of the sequence, starting with 17.

%p branch:= proc(m,dm, bestyet)

%p local t,x, nby,r;

%p nby:= bestyet;

%p for t from F[m][2] by -1 to 0 do

%p x:= dm*F[m][1]^t;

%p if x >= nby then next

%p elif x >= c then nby:= x

%p elif (x*R[m] < c) or (m=nF) then break

%p else nby:= branch(m+1,x,nby);

%p fi

%p od;

%p nby

%p end proc:

%p P:= 17: A[1]:= 17:

%p for n from 2 to 15 do

%p c:= ceil(1/2+1/2*sqrt(5+4*P));

%p while not type(c,integer) do Digits:= 2*Digits; c:= eval(c) od:

%p F:= ifactors(P)[2]; nF:= nops(F);

%p F:= sort(F,(s,t)->s[1]>t[1]);

%p R:= [seq(mul(F[i][1]^F[i][2],i=j+1..nF),j=1..nF)];

%p d:= branch(1,1,P);

%p A[n]:= d - P/d;

%p P:= P*A[n]

%p od:

%p seq(A[n],n=1..15); # _Robert Israel_, May 20 2015

%o (PARI) p=17; print1(p,","); for(n=1,13,r=floor(sqrt(p)); d1=1; d2=1; nE=omega(p); P=factor(p); E=P[,2]; P=P[,1]; forvec(v=vector(nE,i,[0,E[i]]),x=prod(k=1,nE,P[k]^v[k]); if(x<=r && x>=d2,d1=d2; d2=x,if(x<=d2 && x>=d1,d1=x))); difer=p/d2-d2; if(difer<=1,difer=p/d1-d1); print1(difer","); p*=difer)

%Y Cf. A082120, A003681 (starts with 2, 3), A082124.

%K nonn,hard,more

%O 1,1

%A _Ralf Stephan_, Apr 04 2003

%E a(12) from Herman Jamke (hermanjamke(AT)fastmail.fm), Nov 02 2006

%E a(13) from Herman Jamke (hermanjamke(AT)fastmail.fm), Nov 14 2006

%E a(14) and a(15) from _Robert Israel_, May 20 2015

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified March 28 04:13 EDT 2024. Contains 371235 sequences. (Running on oeis4.)