OFFSET
1,3
COMMENTS
The reverse-alternating sum of a sequence (y_1,...,y_k) is Sum_i (-1)^(k-i) 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: () 19: (3,1,1) 40: (2,4)
1: (1) 20: (2,3) 41: (2,3,1)
2: (2) 21: (2,2,1) 42: (2,2,2)
3: (1,1) 22: (2,1,2) 43: (2,2,1,1)
4: (3) 24: (1,4) 44: (2,1,3)
6: (1,2) 26: (1,2,2) 46: (2,1,1,2)
7: (1,1,1) 27: (1,2,1,1) 47: (2,1,1,1,1)
8: (4) 28: (1,1,3) 48: (1,5)
10: (2,2) 30: (1,1,1,2) 50: (1,3,2)
11: (2,1,1) 31: (1,1,1,1,1) 51: (1,3,1,1)
12: (1,3) 32: (6) 52: (1,2,3)
13: (1,2,1) 35: (4,1,1) 53: (1,2,2,1)
14: (1,1,2) 36: (3,3) 54: (1,2,1,2)
15: (1,1,1,1) 37: (3,2,1) 55: (1,2,1,1,1)
16: (5) 38: (3,1,2) 56: (1,1,4)
MATHEMATICA
stc[n_]:=Differences[Prepend[Join@@Position[ Reverse[IntegerDigits[n, 2]], 1], 0]]//Reverse;
sats[y_]:=Sum[(-1)^(i-Length[y])*y[[i]], {i, Length[y]}];
Select[Range[0, 100], sats[stc[#]]>=0&]
CROSSREFS
These compositions are counted by A116406.
These are the positions of terms >= 0 in A344618.
The version for unreversed alternating sum is A345913.
The opposite (k <= 0) version is A345916.
The strict (k > 0) case is A345918.
A011782 counts compositions.
A097805 counts compositions by alternating (or reverse-alternating) sum.
A236913 counts partitions of 2n with reverse-alternating sum <= 0.
A344610 counts partitions by sum and positive reverse-alternating sum.
A344611 counts partitions of 2n with reverse-alternating sum >= 0.
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 04 2021
STATUS
approved