Reminder: The OEIS is hiring a new managing editor, and the application deadline is January 26.
%I #18 May 20 2020 04:51:23
%S 1,1,2,4,25,416,486098,162537896768,14630088002962344485338,
%T 739175469608148343094159739813706354064860288,
%U 1510514900506035538507690225296812635700094164682321019164564511644297549473776602061398338
%N a(n) = numerator of r(n): r(1)=1, r(n+1) = [b(1,n);b(2,n),...,b(n,n)], a continued fraction of rational terms, where {b(k,n)} is the permutation of the first n terms of {r(k)} such that r(n+1) is minimized.
%H Alois P. Heinz, <a href="/A128774/b128774.txt">Table of n, a(n) for n = 1..14</a>
%e The first 5 terms of {r(k)} are: 1,1,2,4/3,25/18. The continued fraction, whose terms are the permutation of the first 5 terms of {r(k)} which leads to the smallest r(6), is [1;2,1,25/18,4/3] = 416/303.
%p Ltoc := proc(L) numtheory[nthconver](L,nops(L)-1) ; end: r := proc(n) option remember ; local m,rL,rp,L ; if n = 1 then 1; else rL := [seq(procname(i),i=1..n-1)] ; rp := combinat[permute](rL) ; m := Ltoc(rL) ; for L in rp do m := min(m, Ltoc(L)) ; od: m ; fi; end: A128774 := proc(n) numer(r(n)) ; end: for n from 1 do printf("%d,\n", A128774(n)) ; od: # _R. J. Mathar_, Jul 30 2009
%p tor:= proc(l) local j; infinity; for j from nops(l) to 1 by -1 do l[j]+1/% od end: hs:= proc(l) local ll, h, s, m; ll:= []; h:= nops(l); s:= 1; m:= s; while s<=h do ll:= [ll[], l[m]]; if m=h then h:= h-1; m:= s else s:= s+1; m:= h fi od; ll end: r:= proc(n) option remember; local j; `if`(n=1, 1, tor(hs(sort([seq(r(j), j=1..n-1)])))) end: a:= n-> numer(r(n)): seq(a(n), n=1..12); # _Alois P. Heinz_, Aug 04 2009
%t r[1] = r[2] = 1;
%t r[n_] := r[n] = FromContinuedFraction /@ Permutations[Array[r, n-1]] // Min;
%t Table[a[n] = Numerator[r[n]]; Print[n, " ", a[n]]; a[n], {n, 1, 11}] (* _Jean-François Alcover_, May 20 2020 *)
%Y Cf. A128772, A128773, A128775.
%K frac,nonn
%O 1,3
%A _Leroy Quet_, Mar 27 2007
%E 3 more terms from _R. J. Mathar_, Jul 30 2009
%E a(10)-a(11) from _Alois P. Heinz_, Aug 04 2009