A335477 - OEIS

%I #9 Jun 30 2020 01:55:59

%S 21,43,45,53,73,85,86,87,91,93,107,109,117,146,147,149,153,165,169,

%T 171,172,173,174,175,181,182,183,187,189,201,213,214,215,219,221,235,

%U 237,245,273,277,293,294,295,297,299,301,306,307,309,313,325,329,331,333

%N Numbers k such that the k-th composition in standard order (A066099) matches the pattern (2,2,1).

%C A composition of n is a finite sequence of positive integers summing to n. 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.

%C We define a pattern to be a finite sequence covering an initial interval of positive integers. Patterns are counted by A000670 and ranked by A333217. A sequence S is said to match a pattern P if there is a not necessarily contiguous subsequence of S whose parts have the same relative order as P. For example, (3,1,1,3) matches (1,1,2), (2,1,1), and (2,1,2), but avoids (1,2,1), (1,2,2), and (2,2,1).

%H Wikipedia, <a href="https://en.wikipedia.org/wiki/Permutation_pattern">Permutation pattern</a>

%H Gus Wiseman, <a href="/A102726/a102726.txt">Sequences counting and ranking compositions by the patterns they match or avoid.</a>

%H Gus Wiseman, <a href="https://docs.google.com/document/d/e/2PACX-1vTCPiJVFUXN8IqfLlCXkgP15yrGWeRhFS4ozST5oA4Bl2PYS-XTA3sGsAEXvwW-B0ealpD8qnoxFqN3/pub">Statistics, classes, and transformations of standard compositions</a>

%e The sequence of terms together with the corresponding compositions begins:

%e    21: (2,2,1)

%e    43: (2,2,1,1)

%e    45: (2,1,2,1)

%e    53: (1,2,2,1)

%e    73: (3,3,1)

%e    85: (2,2,2,1)

%e    86: (2,2,1,2)

%e    87: (2,2,1,1,1)

%e    91: (2,1,2,1,1)

%e    93: (2,1,1,2,1)

%e   107: (1,2,2,1,1)

%e   109: (1,2,1,2,1)

%e   117: (1,1,2,2,1)

%e   146: (3,3,2)

%e   147: (3,3,1,1)

%t stc[n_]:=Reverse[Differences[Prepend[Join@@Position[Reverse[IntegerDigits[n,2]],1],0]]];

%t Select[Range[0,100],MatchQ[stc[#],{___,x_,___,x_,___,y_,___}/;x>y]&]

%Y The complement A335524 is the avoiding version.

%Y The (1,2,2)-matching version is A335475.

%Y Patterns matching this pattern are counted by A335509 (by length).

%Y Permutations of prime indices matching this pattern are counted by A335453.

%Y These compositions are counted by A335472 (by sum).

%Y Constant patterns are counted by A000005 and ranked by A272919.

%Y Permutations are counted by A000142 and ranked by A333218.

%Y Patterns are counted by A000670 and ranked by A333217.

%Y Non-unimodal compositions are counted by A115981 and ranked by A335373.

%Y Combinatory separations are counted by A269134.

%Y Patterns matched by standard compositions are counted by A335454.

%Y Minimal patterns avoided by a standard composition are counted by A335465.

%Y Cf. A034691, A056986, A108917, A114994, A238279, A333224, A333257, A335446, A335456, A335458.

%K nonn

%O 1,1

%A _Gus Wiseman_, Jun 18 2020