A345907 - OEIS

A345907

Triangle giving the main antidiagonals of the matrices counting integer compositions by length and alternating sum (A345197).

1, 1, 1, 0, 1, 1, 0, 1, 1, 1, 0, 2, 2, 1, 1, 0, 0, 4, 3, 1, 1, 0, 0, 3, 6, 4, 1, 1, 0, 0, 6, 9, 8, 5, 1, 1, 0, 0, 0, 18, 18, 10, 6, 1, 1, 0, 0, 0, 10, 36, 30, 12, 7, 1, 1, 0, 0, 0, 20, 40, 60, 45, 14, 8, 1, 1, 0, 0, 0, 0, 80, 100, 90, 63, 16, 9, 1, 1

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OFFSET

0,12

COMMENTS

The matrices (A345197) count the integer compositions of n of length k with alternating sum i, where 1 <= k <= n, and i ranges from -n + 2 to n in steps of 2. Here, the alternating sum of a sequence (y_1,...,y_k) is Sum_i (-1)^(i-1) y_i.

Problem: What are the column sums? They appear to match A239201, but it is not clear why.

LINKS

Table of n, a(n) for n=0..77.

EXAMPLE

Triangle begins:

1 1

0 1 1

0 1 1 1

0 2 2 1 1

0 0 4 3 1 1

0 0 3 6 4 1 1

0 0 6 9 8 5 1 1

0 0 0 18 18 10 6 1 1

0 0 0 10 36 30 12 7 1 1

0 0 0 20 40 60 45 14 8 1 1

0 0 0 0 80 100 90 63 16 9 1 1

0 0 0 0 35 200 200 126 84 18 10 1 1

0 0 0 0 70 175 400 350 168 108 20 11 1 1

0 0 0 0 0 350 525 700 560 216 135 22 12 1 1

MATHEMATICA

ats[y_]:=Sum[(-1)^(i-1)*y[[i]], {i, Length[y]}];

Table[Table[Length[Select[Join@@Permutations/@IntegerPartitions[n, {n-k}], k==(n+ats[#])/2-1&]], {k, 0, n-1}], {n, 0, 15}]

CROSSREFS

Row sums are A163493.

Rows are the antidiagonals of the matrices given by A345197.

The main diagonals of A345197 are A346632, with sums A345908.

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).

Other diagonals are A008277 of A318393 and A055884 of A320808.

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, A007318, A008549, A025047, A114121, A344610.

Sequence in context: A090477 A349802 A368753 * A293019 A376590 A087479

Adjacent sequences: A345904 A345905 A345906 * A345908 A345909 A345910

KEYWORD

nonn,tabl

AUTHOR

Gus Wiseman, Jul 26 2021

STATUS

approved