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A345913
Numbers k such that the k-th composition in standard order (row k of A066099) has alternating sum >= 0.
30
0, 1, 2, 3, 4, 5, 7, 8, 9, 10, 11, 13, 14, 15, 16, 17, 18, 19, 21, 22, 23, 26, 28, 29, 31, 32, 33, 34, 35, 36, 37, 38, 39, 41, 42, 43, 44, 45, 46, 47, 50, 52, 53, 55, 56, 57, 58, 59, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 73, 74, 75, 76, 77, 78, 79, 82
OFFSET
1,3
COMMENTS
The alternating sum of a sequence (y_1,...,y_k) is Sum_i (-1)^(i-1) y_i.
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.
EXAMPLE
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) 39: (3,1,1,1)
3: (1,1) 21: (2,2,1) 41: (2,3,1)
4: (3) 22: (2,1,2) 42: (2,2,2)
5: (2,1) 23: (2,1,1,1) 43: (2,2,1,1)
7: (1,1,1) 26: (1,2,2) 44: (2,1,3)
8: (4) 28: (1,1,3) 45: (2,1,2,1)
9: (3,1) 29: (1,1,2,1) 46: (2,1,1,2)
10: (2,2) 31: (1,1,1,1,1) 47: (2,1,1,1,1)
11: (2,1,1) 32: (6) 50: (1,3,2)
13: (1,2,1) 33: (5,1) 52: (1,2,3)
14: (1,1,2) 34: (4,2) 53: (1,2,2,1)
15: (1,1,1,1) 35: (4,1,1) 55: (1,2,1,1,1)
16: (5) 36: (3,3) 56: (1,1,4)
MATHEMATICA
stc[n_]:=Differences[Prepend[Join@@Position[Reverse[IntegerDigits[n, 2]], 1], 0]]//Reverse;
ats[y_]:=Sum[(-1)^(i-1)*y[[i]], {i, Length[y]}];
Select[Range[0, 100], ats[stc[#]]>=0&]
CROSSREFS
These compositions are counted by A116406.
These are the positions of terms >= 0 in A124754.
The version for prime indices is A344609.
The reverse-alternating sum version is A345914.
The opposite (k <= 0) version is A345915.
The strict (k > 0) version is A345917.
The complement is A345919.
A000041 counts partitions of 2n with alternating sum 0, ranked by A000290.
A011782 counts compositions.
A097805 counts compositions by alternating (or reverse-alternating) sum.
A103919 counts partitions by sum and alternating sum (reverse: A344612).
A316524 gives the alternating sum of prime indices (reverse: A344616).
A345197 counts compositions by sum, length, and alternating sum.
Standard compositions: A000120, A066099, A070939, A228351, A124754, A344618.
Compositions of n, 2n, or 2n+1 with alternating/reverse-alternating sum k:
- k = 0: counted by A088218, ranked by A344619/A344619.
- k = 1: counted by A000984, ranked by A345909/A345911.
- k = -1: counted by A001791, ranked by A345910/A345912.
- k = 2: counted by A088218, ranked by A345925/A345922.
- k = -2: counted by A002054, ranked by A345924/A345923.
- k >= 0: counted by A116406, ranked by A345913/A345914.
- k <= 0: counted by A058622(n-1), ranked by A345915/A345916.
- k > 0: counted by A027306, ranked by A345917/A345918.
- k < 0: counted by A294175, ranked by A345919/A345920.
- k != 0: counted by A058622, ranked by A345921/A345921.
- k even: counted by A081294, ranked by A053754/A053754.
- k odd: counted by A000302, ranked by A053738/A053738.
Sequence in context: A286926 A145198 A083210 * A187392 A232741 A108120
KEYWORD
nonn
AUTHOR
Gus Wiseman, Jul 04 2021
STATUS
approved