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 A243575 Irregular triangular array of numerators of the positive rational numbers ordered as in Comments. 3
 1, 2, 3, 4, 5, 6, 7, 12, 12, 12, 8, 9, 10, 11, 16, 3, 12, 6, 4, 3, 40, 32, 13, 14, 15, 20, 3, 4, 6, 12, 15, 21, 19, 56, 26, 16, 11, 68, 52, 17, 18, 19, 24, 1, 12, 2, 12, 15, 21, 24, 9, 30, 33, 48, 23, 24, 34, 64, 47, 61, 35, 100, 46, 28, 19, 96, 72, 21, 22 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Decree that (row 1) = (1,2,3). For n >=2, row n consists of numbers in increasing order generated as follows: x+4 for each x in row n-1 together with 12/x for each nonzero x in row n-1, where duplicates are deleted as they occur. Every rational number occurs exactly once in the array. The number of numbers in row n is A022095(n-1) for n >= 4. LINKS Clark Kimberling, Table of n, a(n) for n = 1..5000 EXAMPLE First 4 rows of the array of rationals: 1/1 .. 2/1 ... 3/1 4/1 .. 5/1 ... 6/2 . 7/1 . 12/1 12/7 . 12/5 .. 8/1 . 9/1 . 10/1 . 11/1 . 16/1 3/4 .. 12/11 . 6/5 . 4/3 . 3/2 .. 40/7 . 32/5 . 13/1 . 14/1 . 15/1 . 20/1 The numerators, by rows: 1,2,3,4,5,6,7,12,12,12,8,9,10,11,16,3,12,6,4,3,40,32,13,14,15,20. MATHEMATICA z = 10; g[1] = {1, 2, 3}; f1[x_] := x + 4; f2[x_] := 12/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}] v = Flatten[u] Denominator[v] (* A241837 *) Numerator[v] (* A243575 *) CROSSREFS Cf. A241837, A243924, A022095. Sequence in context: A175500 A356253 A222259 * A284447 A032985 A032869 Adjacent sequences: A243572 A243573 A243574 * A243576 A243577 A243578 KEYWORD nonn,easy,tabf,frac AUTHOR Clark Kimberling, Jun 15 2014 STATUS approved

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Last modified July 24 10:37 EDT 2024. Contains 374583 sequences. (Running on oeis4.)