This site is supported by donations to The OEIS Foundation.

 Annual Appeal: Please make a donation to keep the OEIS running. In 2018 we replaced the server with a faster one, added 20000 new sequences, and reached 7000 citations (often saying "discovered thanks to the OEIS"). Other ways to donate

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A226130 Denominators of rational numbers as generated by the rules: 1 is in S, and if nonzero x is in S, then x+1 and -1/x are in S.  (See Comments). 16
 1, 1, 1, 1, 2, 1, 1, 3, 2, 1, 4, 3, 2, 1, 1, 5, 4, 3, 2, 2, 3, 1, 6, 5, 4, 3, 3, 5, 2, 5, 3, 1, 7, 6, 5, 4, 4, 7, 3, 8, 5, 2, 7, 5, 3, 1, 1, 8, 7, 6, 5, 5, 9, 4, 11, 7, 3, 11, 8, 5, 2, 2, 9, 7, 5, 3, 3, 4, 1, 9, 8, 7, 6, 6, 11, 5, 14, 9, 4, 15, 11, 7, 3, 3 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,5 COMMENTS Let S be the set of numbers defined by these rules:  1 is in S, and if nonzero x is in S, then x + 1 and -1/x are in S.  Then S is the set of all rational numbers, produced in generations as follows: g(1) = (1), g(2) = (2, -1), g(3) = (3, -1/2, 0), g(4) = (4,-1/3,1/2),... For n > 4, once g(n-1) = (c(1),...,c(z)) is defined, g(n) is formed from the vector (c(1)+1, -1/c(1), c(2)+1, -1/c(2),...,c(z)+1, -1/c(z)) by deleting previously generated elements.  Let S' denote the sequence formed by concatenating the generations. A226130:  Denominators of terms of S' A226131:  Numerators of terms of S' A226136:  Positions of positive integers in S' A226137:  Positions of integers in S' LINKS Clark Kimberling, Table of n, a(n) for n = 1..1000 EXAMPLE The denominators and numerators are read from the rationals in S': 1/1, 2/1, -1/1, 3/1, -1/2, 0/1, 4/1, -1/3, 1/2, ... MATHEMATICA g[1] := {1}; z = 20; g[n_] := g[n] = DeleteCases[Flatten[Transpose[{# + 1, -1/#}]]&[DeleteCases[g[n - 1], 0]], Apply[Alternatives, Flatten[Map[g, Range[n - 1]]]]]; Flatten[Map[g, Range[7]]]  (* ordered rationals *) Map[g, Range[z]]; Table[Length[g[i]], {i, 1, z}] (* cf. A003410 *) f = Flatten[Map[g, Range[z]]]; Take[Denominator[f], 100] (* A226130 *) Take[Numerator[f], 100]   (* A226131 *) p1 = Flatten[Table[Position[f, n], {n, 1, z}]] (* A226136 *) p2 = Flatten[Table[Position[f, -n], {n, 0, z}]]; Union[p1, p2]  (* A226137 *)  (* Peter J. C. Moses, May 26 2013 *) CROSSREFS Cf. A226080 (rabbit ordering of positive rationals). Sequence in context: A093394 A094363 A124832 * A137569 A266715 A089177 Adjacent sequences:  A226127 A226128 A226129 * A226131 A226132 A226133 KEYWORD nonn,frac AUTHOR Clark Kimberling, May 28 2013 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified December 19 08:25 EST 2018. Contains 318245 sequences. (Running on oeis4.)