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 A243713 Irregular triangular array of numerators of all positive rational numbers ordered as in Comments. 6
 1, 2, 3, 4, 1, 5, 3, 2, 6, 5, 5, 3, 7, 7, 8, 7, 4, 1, 8, 9, 11, 11, 9, 4, 5, 3, 2, 9, 11, 14, 15, 14, 7, 11, 8, 7, 6, 5, 5, 3, 10, 13, 17, 19, 19, 10, 17, 13, 12, 13, 12, 13, 10, 7, 7, 8, 7, 4, 1, 11, 15, 20, 23, 24, 13, 23, 18, 17, 20, 19, 21, 17, 15, 16 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Decree that (row 1) = (1), (row 2) = (3), and (row 3) = (3). Thereafter, row n consists of the following numbers arranged in decreasing order: 1+x for each x in (row n-1), together with x/(x + 1) for each x in row (n-3). Every positive rational number occurs exactly once in the array. The number of numbers in (row n) is A000930(n-1), for n >= 1. LINKS Clark Kimberling, Table of n, a(n) for n = 1..1000 EXAMPLE First 8 rows of the array of all positive rationals: 1/1 2/1 3/1 4/1 ... 1/2 5/1 ... 3/2 ... 2/3 6/1 ... 5/2 ... 5/3 ... 3/4 7/1 ... 7/2 ... 8/3 ... 7/4 ... 4/5 ... 1/3 8/1 ... 9/2 ... 11/3 .. 11/4 .. 9/5 ... 4/3 ... 5/6 ... 3/5 ... 2/5 The numerators, by rows: 1,2,3,4,1,5,3,2,6,5,5,3,7,7,8,7,4,1,8,9,11,11,9,4,5,3,2,... MATHEMATICA z = 13; g[1] = {1}; f1[x_] := x + 1; f2[x_] := -1/x; h[1] = g[1]; b[n_] := b[n] = DeleteDuplicates[Union[f1[g[n - 1]], f2[g[n - 1]]]]; h[n_] := h[n] = Union[h[n - 1], g[n - 1]]; g[n_] := g[n] = Complement [b[n], Intersection[b[n], h[n]]]; u = Table[g[n], {n, 1, z}]; u1 = Delete[Flatten[u], 10] w[1] = 0; w[2] = 1; w[3] = 1; w[n_] := w[n - 1] + w[n - 3]; u2 = Table[Drop[g[n], w[n]], {n, 1, z}]; u3 = Delete[Delete[Flatten[Map[Reverse, u2]], 4], 4] Denominator[u3] (* A243712 *) Numerator[u3] (* A243713 *) Denominator[u1] (* A243714 *) Numerator[u1] (* A243715 *) CROSSREFS Cf. A243712, A243714, A243715, A000930, A243613. Sequence in context: A115994 A276951 A071437 * A332266 A129709 A253146 Adjacent sequences: A243710 A243711 A243712 * A243714 A243715 A243716 KEYWORD nonn,easy,tabf,frac AUTHOR Clark Kimberling, Jun 09 2014 STATUS approved

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Last modified February 21 10:38 EST 2024. Contains 370228 sequences. (Running on oeis4.)