%I A020652
%S A020652 1,1,2,1,3,1,2,3,4,1,5,1,2,3,4,5,6,1,3,5,7,1,2,4,5,7,8,1,3,7,9,1,2,3,4,
               5,
%T A020652 6,7,8,9,10,1,5,7,11,1,2,3,4,5,6,7,8,9,10,11,12,1,3,5,9,11,13,1,2,4,7,
               8,
%U A020652 11,13,14,1,3,5,7,9,11,13,15,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,1,
               5
%N A020652 Numerators in canonical bijection from positive integers to positive 
               rationals.
%D A020652 Richard Courant and Herbert Robbins. What Is Mathematics?, Oxford, 1941, 
               pp. 79-80.
%D A020652 H. Lauwerier, Fractals, Princeton Univ. Press, p. 23.
%H A020652 David Wasserman, <a href="b020652.txt">Table of n, a(n) for n = 1..100000</
               a>
%H A020652 <a href="Sindx_St.html#Stern">Index entries for sequences related to 
               Stern's sequences</a>
%H A020652 <a href="Sindx_Cor.html#core">Index entries for "core" sequences</a>
%e A020652 ..., 1/8, 2/7, 4/5, 5/4, 7/2, 8/1, ...
%p A020652 with (numtheory): A020652 := proc (n) local sum, j, k; sum := 0: k := 
               2: while (sum < n) do: sum := sum + phi(k): k := k + 1: od: sum := 
               sum - phi(k-1): j := 1; while sum < n do: if gcd(j,k-1) = 1 then 
               sum := sum + 1: fi: j := j+1: od: RETURN (j-1): end: # from UlrSchimke(AT)aol.com, 
               Nov 06, 2001
%Y A020652 Essentially the same as A038566, which is the main entry for this sequence.
%Y A020652 Cf. A020653, A038567-A038569.
%Y A020652 A054424 gives mapping to Stern-Brocot tree.
%Y A020652 Sequence in context: A132589 A054843 A038566 this_sequence A096107 A128487 
               A056609
%Y A020652 Adjacent sequences: A020649 A020650 A020651 this_sequence A020653 A020654 
               A020655
%K A020652 nonn,frac,core,nice
%O A020652 1,3
%A A020652 David W. Wilson (davidwwilson(AT)comcast.net)