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%I #4 Jun 14 2014 21:41:42
%S 1,1,1,1,1,1,3,5,1,3,5,3,1,3,5,9,7,3,7,1,3,5,9,7,3,5,7,7,5,2,1,3,5,9,
%T 7,3,5,7,11,7,5,2,19,29,19,13,9,1,3,5,9,7,3,5,7,11,7,5,2,19,29,19,13,
%U 11,17,9,9,17,11,13,19,6,4,5,1,3,5,9,7,3,5
%N Irregular triangular array of denominators of the positive rational numbers ordered as in Comments.
%C Decree that (row 1) = (1). For n >= 2, row n consists of numbers in decreasing order generated as follows: x+1 for each x in row n-1 together with 4/x for each x in row n-1, and duplicates are rejected as they occur. Every positive rational number occurs exactly once in the resulting array.
%H Clark Kimberling, <a href="/A243854/b243854.txt">Table of n, a(n) for n = 1..3000</a>
%e First 6 rows of the array of rationals:
%e 1/1
%e 4/1 ... 2/1
%e 5/1 ... 3/1
%e 6/1 ... 4/3 ... 4/5
%e 7/1 ... 7/3 ... 9/5 ... 2/3
%e 8/1 ... 10/3 ... 14/5 .. 20/9 .. 12/7 .. 5/3 .. 4/7
%e The denominators, by rows: 1,1,1,1,1,1,3,5,1,3,5,3,1,3,5,9,7,3,7.
%t z = 12; g[1] = {1}; f1[x_] := x + 1; f2[x_] := 4/x; h[1] = g[1];
%t b[n_] := b[n] = DeleteDuplicates[Union[f1[g[n - 1]], f2[g[n - 1]]]];
%t h[n_] := h[n] = Union[h[n - 1], g[n - 1]];
%t g[n_] := g[n] = Complement [b[n], Intersection[b[n], h[n]]]
%t u = Table[Reverse[g[n]], {n, 1, z}]; v = Flatten[u];
%t Denominator[v] (* A243854 *)
%t Numerator[v] (* A243855 *)
%t Table[Length[g[n]], {n, 1, z}] (* A243856 *)
%Y Cf. A243855, A243856, A242488, A243848.
%K nonn,easy,tabf,frac
%O 1,7
%A _Clark Kimberling_, Jun 12 2014
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