A345917 Numbers k such that the k-th composition in standard order (row k of A066099) has alternating sum > 0.

1, 2, 4, 5, 7, 8, 9, 11, 14, 16, 17, 18, 19, 21, 22, 23, 26, 28, 29, 31, 32, 33, 34, 35, 37, 38, 39, 42, 44, 45, 47, 52, 56, 57, 59, 62, 64, 65, 66, 67, 68, 69, 70, 71, 73, 74, 75, 76, 77, 78, 79, 82, 84, 85, 87, 88, 89, 90, 91, 93, 94, 95, 100, 104, 105, 107

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.

Links

Table of n, a(n) for n=1..66.

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.

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.

Cf. A000070, A000346, A008549, A025047, A027187, A027193, A032443, A114121, A163493, A344609, A345908.

Sequence in context: A187351 A026451 A050106 * A303739 A183544 A219640

Adjacent sequences: A345914 A345915 A345916 * A345918 A345919 A345920

Keyword

nonn

Author

Gus Wiseman, Jul 08 2021

Status

approved