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A335513
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Numbers k such that the k-th composition in standard order (A066099) avoids the pattern (1,1,1).
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4
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0, 1, 2, 3, 4, 5, 6, 8, 9, 10, 11, 12, 13, 14, 16, 17, 18, 19, 20, 21, 22, 24, 25, 26, 28, 32, 33, 34, 35, 36, 37, 38, 40, 41, 43, 44, 45, 46, 48, 49, 50, 52, 53, 54, 56, 58, 64, 65, 66, 67, 68, 69, 70, 72, 73, 74, 75, 76, 77, 78, 80, 81, 82, 83, 84, 88, 89
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OFFSET
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1,3
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COMMENTS
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These are compositions with no part appearing more than twice.
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.
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).
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LINKS
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EXAMPLE
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The sequence of terms together with the corresponding compositions begins:
0: () 17: (4,1) 37: (3,2,1)
1: (1) 18: (3,2) 38: (3,1,2)
2: (2) 19: (3,1,1) 40: (2,4)
3: (1,1) 20: (2,3) 41: (2,3,1)
4: (3) 21: (2,2,1) 43: (2,2,1,1)
5: (2,1) 22: (2,1,2) 44: (2,1,3)
6: (1,2) 24: (1,4) 45: (2,1,2,1)
8: (4) 25: (1,3,1) 46: (2,1,1,2)
9: (3,1) 26: (1,2,2) 48: (1,5)
10: (2,2) 28: (1,1,3) 49: (1,4,1)
11: (2,1,1) 32: (6) 50: (1,3,2)
12: (1,3) 33: (5,1) 52: (1,2,3)
13: (1,2,1) 34: (4,2) 53: (1,2,2,1)
14: (1,1,2) 35: (4,1,1) 54: (1,2,1,2)
16: (5) 36: (3,3) 56: (1,1,4)
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MATHEMATICA
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stc[n_]:=Reverse[Differences[Prepend[Join@@Position[Reverse[IntegerDigits[n, 2]], 1], 0]]];
Select[Range[0, 100], !MatchQ[stc[#], {___, x_, ___, x_, ___, x_, ___}]&]
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CROSSREFS
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These compositions are counted by A232432 (by sum).
The (1,1)-avoiding version is A233564.
The complement A335512 is the matching version.
Patterns avoiding (1,1,1) are counted by A080599 (by length).
Non-unimodal compositions are counted by A115981 and ranked by A335373.
Combinatory separations are counted by A269134.
Patterns matched by standard compositions are counted by A335454.
Minimal patterns avoided by a standard composition are counted by A335465.
Permutations of prime indices avoiding (1,1,1) are counted by A335511.
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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