A026222 Numbers k such that A026136(k) = A026142(k).

1, 3, 9, 15, 24, 27, 33, 42, 45, 51, 60, 69, 72, 78, 81, 87, 96, 99, 105, 114, 123, 126, 132, 135, 141, 150, 153, 159, 168, 177, 180, 186, 195, 204, 207, 213, 216, 222, 231, 234, 240, 243, 249, 258, 261, 267, 276, 285, 288, 294, 297

Offset: 1

Author

Clark Kimberling

Keywords

• nonn

Links

• Michael De Vlieger, Table of n, a(n) for n = 1..10000
• F. M. Dekking, Permutations of N generated by left-right filling algorithms, arXiv:2001.08915 [math.CO], 2020.

Programs

Mathematica

Block[{nn = 10^3, a, b, s, t}, a[1] = b[1] = 1; Do[If[! IntegerQ[a[#1]], Set[a[#1], i], Set[a[#2], i]] & @@ {i - #, i + #} &@ Floor[i/2], {i, nn}]; s = TakeWhile[Array[a[#] &, nn], IntegerQ]; Do[If[! IntegerQ[b[#1]], Set[b[#1], i], Set[b[#2], i]] & @@ {i - #, i + #} &@ Floor[(i + 1)/2], {i, nn}]; t = TakeWhile[Array[b[#] &, nn], IntegerQ]; Select[Range@ Min[Last /@ {s, t}], s[[#]] == t[[#]] &]] (* Michael De Vlieger, Apr 21 2020 *)