OFFSET
1,2
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 initial terms and the corresponding compositions:
1: (1)
2: (2)
4: (3)
5: (2,1)
7: (1,1,1)
8: (4)
9: (3,1)
11: (2,1,1)
14: (1,1,2)
16: (5)
17: (4,1)
18: (3,2)
19: (3,1,1)
21: (2,2,1)
22: (2,1,2)
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
The version for Heinz numbers of partitions is A026424.
These compositions are counted by A027306.
These are the positions of terms > 0 in A124754.
The weak (k >= 0) version is A345913.
The reverse-alternating version is A345918.
The opposite (k < 0) version is A345919.
A011782 counts compositions.
A097805 counts compositions by alternating (or reverse-alternating) sum.
A345197 counts compositions by sum, length, and alternating sum.
Compositions of n, 2n, or 2n+1 with alternating/reverse-alternating sum k:
KEYWORD
nonn
AUTHOR
Gus Wiseman, Jul 08 2021
STATUS
approved