A257981 Sequence (a(n)) generated by Rule 3 (in Comments) with a(1) = 1 and d(1) = 1.

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

Offset

1,2

Comments

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.

Links

Clark Kimberling, Table of n, a(n) for n = 1..1000

Example

a(1) = 1, d(1) = 1;
a(2) = 3, d(2) = 2;
a(3) = 2, d(3) = -1;
a(4) = 5, d(4) = 3.

Mathematica

{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 *)

Crossrefs

Cf. A257905, A257982.

Sequence in context: A258930 A002797 A049920 * A128914 A050063 A274761

Adjacent sequences: A257978 A257979 A257980 * A257982 A257983 A257984

Keyword

nonn,easy

Author

Clark Kimberling, May 19 2015

Status

approved