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A257981
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Sequence (a(n)) generated by Rule 3 (in Comments) with a(1) = 1 and d(1) = 1.
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3
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1, 3, 2, 5, 10, 4, 8, 6, 12, 7, 14, 11, 22, 9, 18, 36, 13, 26, 15, 30, 16, 32, 17, 34, 24, 20, 40, 19, 38, 21, 42, 23, 46, 28, 56, 25, 50, 41, 29, 58, 31, 62, 27, 54, 47, 39, 78, 33, 66, 37, 74, 35, 70, 44, 88, 45, 90, 43, 86, 48, 96, 52, 104, 49, 98, 57
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OFFSET
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1,2
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COMMENTS
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Rule 3 follows. For k >= 1, let A(k) = {a(1), …, a(k)} and D(k) = {d(1), …, d(k)}. Begin with k = 1 and nonnegative integers a(1) and d(1).
Step 1: If there is an integer h such that 1 - a(k) < h < 0 and h is not in D(k) and a(k) + h is not in A(k), let d(k+1) be the least such h, let a(k+1) = a(k) + h, replace k by k + 1, and repeat Step 1; otherwise do Step 2.
Step 2: Let h be the least positive integer not in D(k) such that a(k) - h is not in A(k). Let a(k+1) = a(k) + h and d(k+1) = h. Replace k by k+1 and do Step 1.
See A257905 for a guide to related sequences and conjectures.
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LINKS
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EXAMPLE
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a(1) = 1, d(1) = 1;
a(2) = 3, d(2) = 2;
a(3) = 2, d(3) = -1;
a(4) = 5, d(4) = 3.
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MATHEMATICA
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{a, f} = {{1}, {1}}; Do[tmp = {#, # - Last[a]} &[Min[Complement[#, Intersection[a, #]]&[Last[a] + Complement[#, Intersection[f, #]] &[Range[2 - Last[a], -1]]]]];
If[! IntegerQ[tmp[[1]]], tmp = {Last[a] + #, #} &[NestWhile[# + 1 &, 1, ! (! MemberQ[f, #] && ! MemberQ[a, Last[a] - #]) &]]]; AppendTo[a, tmp[[1]]]; AppendTo[f, tmp[[2]]], {120}]; {a, f} (* Peter J. C. Moses, May 14 2015 *)
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CROSSREFS
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KEYWORD
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nonn,easy
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AUTHOR
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STATUS
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approved
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