%I A020653
%S A020653 1,2,1,3,1,4,3,2,1,5,1,6,5,4,3,2,1,7,5,3,1,8,7,5,4,2,1,9,7,3,1,10,9,8,
               7,
%T A020653 6,5,4,3,2,1,11,7,5,1,12,11,10,9,8,7,6,5,4,3,2,1,13,11,9,5,3,1,14,13,11,
%U A020653 8,7,4,2,1,15,13,11,9,7,5,3,1,16,15,14,13,12,11,10,9,8,7,6,5,4,3,2,1,17
%N A020653 Denominators in canonical bijection from positive integers to positive 
               rationals.
%D A020653 Richard Courant and Herbert Robbins. What Is Mathematics?, Oxford, 1941, 
               pp. 79-80.
%D A020653 H. Lauwerier, Fractals, Princeton Univ. Press, p. 23.
%H A020653 David Wasserman, <a href="b020653.txt">Table of n, a(n) for n = 1..100000</
               a>
%H A020653 <a href="Sindx_Cor.html#core">Index entries for "core" sequences</a>
%p A020653 with (numtheory): A020653 := 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 (k-j): end: # from UlrSchimke(AT)aol.com, 
               Nov 06, 2001
%Y A020653 Cf. A020652.
%Y A020653 Sequence in context: A079786 A032451 A088445 this_sequence A094522 A118487 
               A091420
%Y A020653 Adjacent sequences: A020650 A020651 A020652 this_sequence A020654 A020655 
               A020656
%K A020653 nonn,frac,core,nice
%O A020653 1,2
%A A020653 David W. Wilson (davidwwilson(AT)comcast.net)