A375138 Numbers k such that the k-th composition in standard order (row k of A066099) matches the dashed pattern 23-1.

41, 81, 83, 105, 145, 161, 163, 165, 166, 167, 169, 209, 211, 233, 289, 290, 291, 297, 321, 323, 325, 326, 327, 329, 331, 332, 333, 334, 335, 337, 339, 361, 401, 417, 419, 421, 422, 423, 425, 465, 467, 489, 545, 553, 577, 578, 579, 581, 582, 583, 593, 595, 617

Offset

1,1

Comments

The k-th composition in standard order (graded reverse-lexicographic, A066099) is obtained by taking the set of positions of 1's in the reversed binary expansion of k, prepending 0, taking first differences, and reversing again. This gives a bijective correspondence between nonnegative integers and integer compositions.

These are also numbers k such that the maximal weakly increasing runs in the reverse of the k-th composition in standard order do not have weakly decreasing leaders, where the leaders of weakly increasing runs in a sequence are obtained by splitting it into maximal weakly increasing subsequences and taking the first term of each.

The reverse version (A375137) ranks compositions matching the dashed pattern 1-32.

Links

Table of n, a(n) for n=1..53.

Wikipedia, Permutation pattern.

Example

Composition 89 is (2,1,3,1), which matches 2-3-1 but not 23-1.
Composition 165 is (2,3,2,1), which matches 23-1 but not 231.
Composition 358 is (2,1,3,1,2), which matches 2-3-1 and 1-3-2 but not 23-1 or 1-32.
The sequence together with corresponding compositions begins:
   41: (2,3,1)
   81: (2,4,1)
   83: (2,3,1,1)
  105: (1,2,3,1)
  145: (3,4,1)
  161: (2,5,1)
  163: (2,4,1,1)
  165: (2,3,2,1)
  166: (2,3,1,2)
  167: (2,3,1,1,1)
  169: (2,2,3,1)
  209: (1,2,4,1)
  211: (1,2,3,1,1)
  233: (1,1,2,3,1)

Mathematica

stc[n_]:=Differences[Prepend[Join @@ Position[Reverse[IntegerDigits[n, 2]], 1], 0]]//Reverse;
Select[Range[0, 100], MatchQ[stc[#], {___, y_, z_, ___, x_, ___}/; x<y<z]&] (*23-1*)

Crossrefs

The complement is too dense, but counted by A189076.

The non-dashed version is A335482, reverse A335480.

For leaders of identical runs we have A335486, reverse A335485.

Compositions of this type are counted by A374636.

The reverse version is A375137, counted by A374636.

Matching 12-1 also gives A375296, counted by A375140 (complement A188920).

A003242 counts anti-runs, ranks A333489.

A011782 counts compositions.

A238130, A238279, A333755 count compositions by number of runs.

All of the following pertain to compositions in standard order:

- Length is A000120.

- Sum is A029837(n+1).

- Leader is A065120.

- Parts are listed by A066099, reverse A228351.

- Number of adjacent equal pairs is A124762, unequal A333382.

- Strict compositions are A233564.

- Constant compositions are A272919.

- Run-length transform is A333627, sum A070939.

- Run-counts: A124766, A124765, A124768, A124769, A333381, A124767.

- Run-leaders: A374629, A374740, A374683, A374757, A374515, A374251.

Cf. A056823, A106356, A188919, A238343, A333213, A335466, A373948, A373953, A374633, A375123, A375139, A374768.

Sequence in context: A044107 A044488 A335482 * A173550 A136072 A098061

Adjacent sequences: A375135 A375136 A375137 * A375139 A375140 A375141

Keyword

nonn

Author

Gus Wiseman, Aug 09 2024

Status

approved